After a long day of talks over the disputed enclave of Nagorno-Karabakh, U.S. Deputy Secretary of State Strobe Talbott was escorted to the airport in Yerevan by Armenian Prime Minister Vazgen Sarkisian. An hour later, Sarkisian was dead, shot at close range in the parliament building across the street from the Armenian president's office, where Talbott had spent the afternoon in negotiations.

The second-highest ranking U.S. diplomat was in that remote corner of the world because he believed that Armenia, one of the biggest per-capita recipients of U.S. foreign aid, was close to resolving a conflict with neighboring Azerbaijan that in the early 1990s cost 30,000 lives, created roughly a million refugees, forced the rerouting of oil pipelines and heightened tensions among Turkey, Russia and Iran.

The shooting of Sarkisian--a former hardliner who had become supportive of a negotiated solution--along with the speaker of the Armenian parliament and several other leading political figures was a setback for the negotiations.

Talbott, who received word of the attack while flying from Armenia to Turkey, declined to discuss the shooting in a brief telephone interview last night. But he said of Sarkisian: "We were just getting to know him."

President Clinton, speaking to reporters on the White House lawn, said, "We've done a lot of work with Armenia and Azerbaijan to try to resolve the difficulties surrounding Nagorno-Karabakh. The two presidents have been very forthcoming, and this is a real blow to that country and to that region, and I'm very sorry about it."

Earlier, Clinton said in a written statement that he was "shocked and saddened" by the attack. "I condemn this senseless act against individuals actively engaged in building democracy in their country," Clinton said.

Senior administration officials said there was no reason to believe the violence was linked to Talbott's talks. A senior official said one of the gunmen, Nairi Unanian, 34, had been a member of an Armenian nationalist group called Dashnak during the late 1980s but was expelled because he was considered too extremist even for that organization.

For Armenian nationalists, Nagorno-Karabakh is an extremely emotional issue. The enclave, populated mostly by Christian Armenians, had been located inside predominantly Muslim Azerbaijan. But Armenia won control of the enclave and about 20 percent of Azerbaijan's territory in fighting between the two former Soviet republics that ended in 1993.

The slain prime minister "was a particularly important figure because he was an individual able to bridge camps traditionally seen as more hard-line in Armenia and others seen as more liberal," said a senior Clinton administration official. Though a one-time opponent of negotiating with Azerbaijan, Sarkisian had recently said he supported the talks and was working closely with Armenian President Robert Kocharian. Both leaders participated in yesterday's talks with Talbott.

Secretary of State Madeleine K. Albright has taken an interest in the Nagorno-Karabakh dispute, spurred in part by an influential lobby of Armenian Americans and by a diplomatic relationship she has maintained with Azerbaijani President Heydar Aliyev since she visited Azerbaijan as the U.S. ambassador to the United Nations, State Department officials said.

Aliyev met with Kocharian in Albright's office on April 26 during the celebration of NATO's 50th anniversary. It was the first direct contact between the Azerbaijani and Armenian presidents. Since then, they have met four more times, including once during the recent U.N. General Assembly session in New York.

A senior administration official said the closely guarded talks were concerned with an exchange of territory, a resolution of conflicting territorial claims, and the resettlement of refugees. The United States, France and Russia co-chair the so-called Minsk group of countries assigned by the Organization for Security and Cooperation in Europe to find a settlement to the dispute. Talbott was exploring what contribution foreign states could make, an official said.

Talbott had met earlier in the day with Aliyev in Baku, the Azerbaijani capital. He then moved on to Yerevan and finished the day in Ankara, the Turkish capital. Turkey maintains close relations with Azerbaijan and has been enforcing a blockade on Armenian goods, which must travel through Iran or the former Soviet republic of Georgia. The slain prime minister, a former Soviet official, has stressed the maintenance of good relations with Moscow as a counterweight to Turkey and Azerbaijan.

U.S. officials said they believe Sarkisian became convinced of the need for a negotiated settlement to Nagorno-Karabakh because the conflict was an obstacle to foreign investment. Multinational oil companies seeking to exploit reserves in the Caspian Sea area are making plans to circumvent Armenia, even though crossing its territory would be one of the most direct routes to export terminals.

In September, Armenian President Kocharian called a meeting with Aliyev "another step forward in the negotiating process," and the two leaders said they had agreed to "confidence building" measures.

State Department officials said yesterday they expect negotiations to continue with Kocharian, who appeared to be in control of the entire country except for the parliament building where the gunmen were still holding hostages.

"Deputy Secretary Talbott is now making an assessment on that very question of how--what the potential is for progress there," said State Department spokesman James P. Rubin.

Correspondent R. Jeffrey Smith contributed to this report from Ankara.

CAPTION: Deputy Secretary of State Strobe Talbott had met with the slain prime minister earlier in the day.