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 American Embassy in Riyadh, Saudi Arabia, reported in February that the Saudis 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.

Last week, American officials said steady pressure from the Bush and Obama administrations had led to significant improvements in fighting terrorist financing. They said, for example, Saudi Arabia was now taking actions that they had long hesitated to take or had resisted, including holding financiers accountable through prosecutions and making terrorist financing a higher priority. A leading Saudi religious scholar has issued an edict against terrorist financing, and the Saudis have created new financial intelligence unit.