A high-powered U.S. government delegation, including top experts on several aspects of Iranian affairs, made unusually secretive visits this week to Western European leaders, State Department sources said yesterday.

The only Washington announcement of the trip was a vague, one-paragraph statement by the State Department last Sunday that "Deputy Secretary of State Warren Christopher, accompanied by senior State Department and National Security Council representatives, will meet in Bonn early this week with Foreign Office State Secretary Guenther van Weil and other officials for a review of key foreign policy issues of interest to the two countries.

In fact, Christopher met with West German Chancellor Helmut Schmidt, French President Valery Giscard d'Estaing and British Prime Minister Margaret Thatcher, among others.

Accompanying Christopher, though unmentioned in the U.S. annoncement, were Deputy Treasury Secretary Robert Caswell, the government's senior expert on Iranian financial assets and sanctions; Assistant Secretary of State for Near Eastern and South Asian Affairs Harold H. Saunders, whose reponsibilities include both Iran and Afghanistan; State Department legal advisor Roberts B. Owen, who represented the United States in the World Court case against Iran's taking of American hostages, and Arnold L. Raphel, the Iran expert in the executive office of Secretary of State Edmund Muskie.

Tight-lipped officials said Iran was among the topics discussed. The sources insisted that there was "absolutely" no contact, directly or indirectly," between the U.S. team and Iranian Central Bank Governor Ali Reza Nobari, a close aide of Iranian President Abol Hassan Beni-Sadr, who also turned up this week in Bonn, where the Washington mission spent most of its time.

The sources went out of their way to discourage any idea that the discussions about Iran have brought Washington and Tehran close to a breakthrough on ending the 10 1/2-month captivity of American diplomatic personnel.

While refusing to give any details of the discussions about Iran, and providing even general information on the trip only reluctanly and piece-meal, the sources said that the team returned from Europe with no encouragement on the hostage issue.

Since Iran's Ayatollah Ruhollah Khomeini spoke a week ago yesterday of a limited set of demands to be satisfied before release of the Americans, work within the U.S. government has intensified on possible ways to meet those demands. Khomeini's announced conditions, and resulting U.S. studies, concentrated in the financial area. The demands included return of the late Shah Mohammad Reza Pahlavi's assets to Iran, cancellation of financial claims against Iran and freeing of Iranian assets frozen by the United States.

A flurry of optimism among high officials after Khomeini's statement late last week was short-lived. According to several officials, the sudden escalation of tension between Iran and neighboring Iraq, including Iraqi cancellation of a 1975 agreement settling the two nation's border dispute, has set back hopes that Iran's parliament and other political forces are at last ready to negotiate release of the Americans.

There are strong indications that some high U.S. officials hope that the tension with Iraq, which flared up early this week, will subside quickly or that the issue will be surmounted in the weeks ahead by those in Tehran who seek an early settlement of the hostage issue.

It is clear that officials have not discarded the possiblity of a breakthrough in the hostage crisis before the Nov. 4 elections. There were hints that recent efforts, including this week's high-level mission, had been expected to produce more than they did.

Muskie, speaking to reporters late yesterday, confirmed the existence of a lengthy collection of official documents for use in the event that a commission of inquiry is convened to examine U.S.-Iranian relations. Muskie called the papers, first reported in yesterday's Washington Post, "an inventory of papers" rather than a "document." Other than Muskie's brief remarks, the State Department had nothing new to say about the Iran papers yesterday.

In addition to Iran questions, the Christopher agenda in Europe included high-level consideration of the Afghanistan situation and allied economic sanctions against the Soviet Union because of its invasion of that country, as well as next week's discussion in New York between Muskie and Soviet Foreign Minister Andrei A. Gromyko on medium-range nuclear missiles in Europe.

Among the items discussed in Bonn and Paris were recently concluded deals by German and French firms to sell the Soviets large-scale industrial facilities of the type U.S. firms had discussed with the Russians before the invasion of Afghanistan. In both cases, the U.S. companies lost the chance for contracts of more than $800 million because U.S. sanctions against the Russians forced them to withdraw from negotiations.

In addition to the officials named above, Christopher was accompanied in Europe by George Vest, assistant secretary of state for European affairs; Reginald Batholemew, State Department director of politico-military affairs, and Robert Blackwell, Western European specialist of the National Security Council.

Christopher left Washington last Sunday and returned late Thursday.