On Nov. 18, for the first time since 1975, a team of American experts will explore the site of a crashed U.S. warplane in Vietnam. A high Pentagon official voiced hope yesterday that Hanoi will continue to cooperate in accounting for 1,797 Americans still listed as missing in action during the Vietnam war.

Richard L. Armitage, assistant secretary of defense for international security affairs, announced the agreement under which 11 Americans will join 10 Vietnamese in excavating the site where a U.S. Air Force B52 bomber crashed in a rice paddy north of Hanoi in December 1972.

Identifying the plane and its crew is expected to take about 10 days and cost about $150,000, Armitage said. A B52 normally has a crew of six men.

Armitage also said that U.S. and Vietnamese negotiators plan a technical meeting on Wednesday in Hanoi -- the fifth such meeting this year -- to "discuss and exchange information relating to the prisoner-of-war and missing-in-action issues."

In addition, Armitage said, Hanoi has agreed to turn over "in the near future" the remains of seven men believed to be Americans. Hanoi already has repatriated the remains of 26 Americans, five of whom were officially identified yesterday.

They five were: Navy Lt. j.g. Richard C. Sather of Pomona, Calif., who was 26 when he became the first American shot down over North Vietnam on Aug. 5, 1964; Navy Cmdr. Randolph W. Ford of Gainesville, Fla., who was 34 when he was shot down over North Vietnam on June 11, 1968; Army Sgt. Richard F. Williams of San Leandro, Calif., 40 when reported missing in South Vietnam on Jan. 8, 1968; Marine Sgt. Joseph S. Zawtocki Jr. of Utica, N.Y., 21 when reported missing in South Vietnam on Feb. 8, 1968, and Army Cpl. Francis E. Cannon, of Phoenix, 23 when he disappeared in South Vietnam on Jan. 8, 1968.

In a related area, Armitage said, the Vietnamese delegation to the United Nations will meet Monday in New York with a representative of the National League of Prisoner of War and Missing in Action Families.

Armitage said the government of Laos, where 556 Americans are listed as unaccounted for, has agreed in principle to early excavation of "possibly more than one site," in addition to one explored last February in which 13 bodies were recovered.