HANOI, Vietnam (AP) _ U.S. and Vietnamese officials celebrated the opening today of the first American liaison office in Vietnam since the end of the war 20 years ago.

The United States and Vietnam established liaison offices in each other's capitals by signing an agreement earlier in the day to return or pay for diplomatic properties seized when the Vietnam War ended in 1975. The offices represent a major stride toward full diplomatic relations for the former foes.

James Hall, a former U.S. Army captain and veteran of the war, will head the liaison office in Hanoi. He greeted two dozen American businessmen, reporters and others who mostly empty nine-story glass tower housing the new U.S. office.

``Today's the day to move in furniture,'' Hall said. ``We'll do the flag-raising some time after Tet.''

The Vietnamese festival for Tet, the Lunar New Year, ends on Thursday.

Chris Runckel, Hall's deputy, said the liaison office would open for business Friday. The office still lacked an identification plaque, but that would soon change, Runckel said.

The liaison offices will fill consular, political and economic functions and probably serve as a transitional step toward the establishment of embassies. The U.S. office will also support efforts to learn the fate of 1,621 American servicemen listed as missing in Vietnam.

President Clinton has said Vietnam must do more to help on the MIA issue before the United States agrees to exchange ambassadors. But the decision to open liaison offices demonstrates Washington's approval of Vietnamese efforts so far.

U.S. diplomats wouldn't say when they thought the United States might establish full relations with Vietnam. Washington eventually upgraded its liaison offices in both China and Angola to embassies, they said.

Hall told reporters that achieving progress on missing servicemen was the top priority for the U.S. liaison office.

Hall signed the diplomatic properties agreement with Nguyen Xuan Phong, director of the Americas Department at Vietnam's Foreign Ministry. Under the agreement, Vietnam agreed to return 10 of the 36 original U.S. buildings and pay an undisclosed amount of cash for the others, said a Vietnamese diplomat, who spoke on condition of anonymity.

Hanoi took possession in Washington of the former South Vietnamese embassy building, which it plans to use as its liaison office.

U.S.-Vietnam relations began to warm when Clinton agreed in July 1993 to stop blocking Hanoi's access to international development loans. He lifted the 19-year U.S. economic embargo against Vietnam last February, and more than 50 American companies have already set up shop here.

U.S. businessmen based in Hanoi welcomed the opening of the liaison office.

``More American companies will come here because people will have confidence that business will be promoted and protected,'' said Norris Hickerson, country manager in Vietnam for Digital Equipment Corp.