WASHINGTON — Nine years after the United States vowed to shut down the money pipeline that finances terrorism, senior Obama administration officials say they believe that many millions of dollars are flowing largely unimpeded to extremist groups worldwide, and they have grown frustrated by frequent resistance from allies in the Middle East, according to secret diplomatic dispatches.

The government cables, sent by Secretary of State Hillary Rodham Clinton and senior State Department officials, catalog a long list of methods that American officials suspect terrorist financiers are using, from a brazen armed bank robbery in Yemen last year to kidnappings for ransom, drug proceeds in Afghanistan and annual religious pilgrimages to Mecca, where millions of riyals or other forms of currency change hands.

While American officials in their public statements have been relatively upbeat about their progress in disrupting terrorist financing, the internal State Department cables, obtained by WikiLeaks and made available to several news organizations, offer a more pessimistic account, with blunt assessments of the threats to the United States from money flowing to militants affiliated with Al Qaeda, the Taliban, Hamas, Lashkar-e-Taiba and other groups.

A classified memo sent by Mrs. Clinton last December made it clear that residents of Saudi Arabia and its neighbors, all allies of the United States, are the chief financial supporters of many extremist activities. “It has been an ongoing challenge to persuade Saudi officials to treat terrorist financing emanating from Saudi Arabia as a strategic priority,” the cable said, concluding that “donors in Saudi Arabia constitute the most significant source of funding to Sunni terrorist groups worldwide.”

The dispatch and others offered similarly grim views about the United Arab Emirates (“a strategic gap” that terrorists can exploit), Qatar (“the worst in the region” on counterterrorism) and Kuwait (“a key transit point”). The cable stressed the need to “generate the political will necessary” to block money to terrorist networks — groups that she said were “threatening stability in Pakistan and Afghanistan and targeting coalition soldiers.”

While President George W. Bush frequently vowed to cut off financing for militants and pledged to make financiers as culpable as terrorists who carried out plots, President Obama has been far less vocal on the issue publicly as he has sought to adopt a more conciliatory tone with Arab nations. But his administration has used many of the same covert diplomatic, intelligence and law enforcement tools as his predecessor and set up a special task force in the summer of 2009 to deal with the growing problem.

While federal officials can point to some successes — prosecutions, seizures of money and tightened money-laundering regulations in foreign countries — the results have often been frustrating, the cables show. As the United States has pushed for more aggressive crackdowns on suspected supporters of terrorism, foreign leaders have pushed back. In private meetings, they have accused American officials of heavy-handedness and of presenting thin evidence of wrongdoing by Arab charities or individuals, according to numerous State Department cables.

Kuwaiti officials, for example, resisted what they called “draconian” measures sought by the United States against a prominent charity and dismissed allegations against it as “unconvincing,” according to one cable.

The documents are filled with secret government intelligence on possible terrorist-financing plots, like the case of a Somali preacher who was reportedly touring Sweden, Finland and Norway last year to look for money and recruits for the Shabab, a militant group in Somalia, or that of a Pakistani driver caught with about $240,000 worth of Saudi riyals stuffed behind his seat. One memo even reported on a possible plot by the Iranians to launder $5 billion to $10 billion in cash through the Emirates’ banks as part of a broader effort to “stir up trouble” among the Persian Gulf states, though it was not clear how much of the money might be channeled to militants.

One episode that set off particular concern occurred in August 2009 in Yemen, when armed robbers stormed a bank truck on a busy downtown street in Aden during daylight hours and stole 100 million Yemeni riyals, or about $500,000. American diplomats said the sophistication of the robbery and other indicators had all the markings of a Qaeda mission. “This bold, unusual operation” could provide Al Qaeda “with a substantial financing infusion at a time when it is thought to be short of cash,” a dispatch summarizing the episode said.

Al Qaeda’s branch in Yemen, known as Al Qaeda in the Arabian Peninsula, is seen as a rising threat by the United States and was blamed for a parcel bomb plot in October and the failed attempt to blow up a jetliner last Dec. 25. The cables do not make clear how or whether the finances of the Yemen group are tied to the network led by Osama bin Laden, whose members are believed to be in hiding along the Pakistan-Afghanistan border.

American officials appear to have divided views on the bin Laden group’s fund-raising abilities. A cable sent in February of this year to Richard C. Holbrooke, the Obama administration’s special representative for Afghanistan and Pakistan, said that “sensitive reporting indicates that al-Qaida’s ability to raise funds has deteriorated substantially, and that it is now in its weakest state since 9/11.”

But many other State Department cables draw the opposite conclusion and cite the group’s ability to generate money almost at will from wealthy individuals and sympathetic groups throughout the Middle East while often staying a step ahead of counterterrorism officials.

“Terrorists avoid money transfer controls by transferring amounts below reporting thresholds and using reliable cash couriers, hawala, and money grams,” a recent cable warned. “Emerging trends include mobile banking, pre-paid cards, and Internet banking.”

The documents suggest that there is little evidence of significant financial support in the United States or Europe for terrorist groups in Afghanistan and Pakistan, despite a string of deadly but largely low-budget attacks in London and other European cities in recent years, according to the documents.

“U.K. financing is important, but the real money is in the Gulf,” a senior British counterterrorism official told a Treasury Department official, according to a cable last year from the American Embassy in London.

In hundreds of cables focusing on terrorist financing, the problem takes on an air of intractability, as American officials speak of the seeming ease with which terrorists are able to move money, the low cost of carrying out deadly attacks, and the difficulty of stopping it. Interdictions are few, and resistance is frequent.

In Kuwait, for instance, American officials have voiced repeated concerns that Islamic charities — largely unregulated by the government there — are using philanthropic donations to finance terrorism abroad. But a Kuwaiti minister, in a meeting last year with the United States ambassador, “was as frank and pessimistic as ever when it came to the subject of apprehending and detaining terror financiers and facilitators under Kuwait’s current legal and political framework,” a memo summarizing the meeting said.

Saudi Arabia, a critical military and diplomatic ally, emerges in the cables as the most vexing of problems. Intelligence officials there have stepped up their spying on militants in neighboring Yemen, and they provided the tip that helped uncover the recent parcel bombs. But while the Saudis have made some progress, “terrorist funding emanating from Saudi Arabia remains a serious concern,” according to a cable in February. Mrs. Clinton’s memo two months earlier said Al Qaeda, the Taliban, Lashkar-e-Taiba and other groups “probably raise millions of dollars annually from Saudi sources, often during Hajj and Ramadan.” Officials said they believed that fund-raisers for extremist groups had often descended on the pilgrims to seek money for their causes.

The United States Embassy in Riyadh, Saudi Arabia, reported in February that the Saudi authorities remained “almost completely dependent on the C.I.A.” for leads and direction on terrorist financing.

So it was not surprising that a month earlier, the embassy reported in a separate cable that Treasury Department officials had provided information to the Saudi domestic intelligence service, the Mabahith, on three senior Taliban leaders — Tayyeb Agha, Mullah Jalil and Khalil Haqqani — who had made several fund-raising trips to the kingdom, the cable said. (Like a number of other suspected financiers identified in the cables, the three Taliban leaders do not appear on the Treasury Department’s list of “banned” entities suspected of terrorism financing connections.)

The Americans shared phone numbers, e-mail addresses and passport information for the three men with the Saudis to cross check against Saudi customs databases. Saudi authorities said they were not familiar with the Taliban leaders but promised to pursue the tips.

In conversations last week, Obama administration officials said that since the latest cable released from WikiLeaks, from February 2010, the Saudis had made notable progress, including the arrests of some major donors to terrorist groups. Despite such pledges of cooperation between the countries, tensions have occasionally flared behind the scenes. In 2007, a senior Bush administration official, Frances Fragos Townsend, told her Saudi counterparts in Riyadh that Mr. Bush was “quite concerned” about the level of cooperation from the Saudis on terrorist financing, and she brought a personal letter on the subject from the president to King Abdullah, according to a cable summarizing the exchange.

Ms. Townsend questioned whether the kingdom’s ambassador to the Philippines, Mohammed Ameen Wali, might be involved in supporting terrorism because of his involvement with two people suspected of being financiers, the summary said.

Prince Saud al-Faisal, the Saudi foreign minister, challenged the assertion, however, saying the ambassador might be guilty of “bad judgment rather than intentional support for terrorism,” and he countered with an assertion of his own: an unnamed American bank handling the Saudi Embassy’s money in Washington was performing unnecessary audits and asking “inappropriate and aggressive questions.”

American diplomats said that while the Saudis appeared earnest in wanting to stanch the flow of terrorist money, they often lacked the training and expertise to do it. “Their capabilities often fall short of their aspirations,” a cable last November said.

Saudi leaders appear equally resigned to the situation, according to the cables. “We are trying to do our best,” Prince Mohammed bin Nayef, who leads the Saudis’ anti-terrorism activities, was quoted as telling Mr. Holbrooke, the special representative to the region, in a May 2009 meeting.

But, he said, “if money wants to go” to terrorist causes, “it will go.”