Tuesday's military coup in Pakistan reflects the steady erosion of American influence on Islamabad, once a trusted Cold War ally whose officers trained in Kansas while their leaders were feted at the White House and on Capitol Hill.

Throughout the 1980s, Washington worked hand-in-glove with Pakistan, a staging area for the CIA-backed holy warriors who drove the Soviet Union from Afghanistan. More recently, however, the relationship has cooled, a consequence of shifting strategic priorities and Washington's decision to punish Pakistan for its nuclear program by severing most military and economic ties between the two countries.

Some analysts and lawmakers, in fact, cite the bloodless coup led by Gen. Pervaiz Musharraf, the army chief of staff, as evidence that U.S. sanctions against Pakistan have backfired--depriving Washington of its ability to shape events when it matters most. In recent weeks, the United States issued public and private warnings to the Pakistani military--including a personal phone call to Musharraf from Marine Gen. Anthony Zinni, chief of the U.S. Central Command--in an unsuccessful effort to forestall the army takeover.

Washington is hardly without influence in Pakistan. In July, after an extraordinary personal appeal from President Clinton, Prime Minister Nawaz Sharif ordered Musharraf to withdraw Pakistani forces from the Kargil region of Kashmir. Musharraf reluctantly complied, defusing an escalating military confrontation with India.

But many policymakers see a larger lesson in Sharif's ouster. "I think the United States should have been far more engaged during the past 10 years, and if we had been, then we would have been in a far better position today than we are," said Sen. Sam Brownback (R-Kan.), chairman of the Senate Foreign Relations subcommittee on Near Eastern and South Asian affairs, who like many farm state lawmakers is also concerned about the effect of trade sanctions on U.S. commodity exports.

Administration officials concede the point, noting that Clinton had asked Congress for--and, before the coup, appeared set to receive--the authority to permanently waive the sanctions imposed on India and Pakistan after their back-to-back nuclear tests last year.

"The decade of . . . sanctions has steadily reduced our influence, both in terms of having officers trained in the United States and in terms of confidence and trust in the United States by the Pakistani people," a senior administration official said. "One of the things we'd been trying to do with Sharif over the last year was to try to rebuild some of those ties."

But the coup may actually increase Pakistan's isolation: On Tuesday, Rep. Benjamin A. Gilman (R-N.Y.), chairman of the House International Relations Committee, said Congress should rethink its decision to grant Clinton the authority to waive restrictions on military relations with Pakistan. At the International Monetary Fund, meanwhile, officials said they were taking a second look at a $1.5 billion loan to Pakistan approved in 1997.

Administration officials said yesterday that they have had no direct contact with Musharraf, and they reiterated pleas for the restoration of democracy. "What we hope very much is there is a return to a constitutional system in Pakistan and that we are able to continue the work that we have been doing to deflect the conflict, to talk again about solving the Kashmir problem peacefully," Secretary of State Madeleine K. Albright said after delivering a speech at the University of Maine.

Military ties have defined the U.S.-Pakistan relationship since the 1950s. Frances Gary Powers, the U-2 pilot shot down over the Soviet Union in 1960, took off from a base in the northern city of Peshawar.

But there have been rough patches before. Pakistan's pursuit of nuclear weapons, for example, triggered the first set of sanctions in the late 1970s. But the Soviet invasion of Afghanistan invested the relationship with a new strategic rationale. The United States trained hundreds of Pakistani officers and sold the country advanced weaponry, including F-16 fighters.

With the end of the Cold War, U.S. officials could no longer ignore Pakistan's nuclear ambitions and, in 1990, imposed sweeping sanctions under legislation named for former senator Larry Pressler. Arms sales stopped--the United States canceled the delivery of 60 additional F-16s that Pakistan had already paid for--and so did military training.

Although Washington maintained cordial relations with Sharif's predecessor, Benazir Bhutto, administration officials and some lawmakers contend that the severing of military ties had the unintended effect of weakening U.S. influence over Pakistan's most important institution. The erosion of that influence, moreover, occurred at a time of mounting U.S. concern about Islamic extremists in the Pakistani armed forces and evidence of drug trafficking by some officers.

U.S. officials tried to rebuild that influence by, among other actions, releasing funds last year that Pakistan had paid for the undelivered fighter jets. But other developments seemed to work against their efforts.

Several officials noted that Musharraf's predecessor as chief of staff, Gen. Jehangir Karamat, who was dismissed last year by Sharif, received military training at Fort Leavenworth, Kan., and had a close relationship with Gen. Joseph Ralston, vice chairman of the Joint Chiefs of Staff. Musharraf, by contrast, trained in Britain and is relatively unknown here.

"We've lost basically a generation of Pakistani officers," a U.S. military officer said.