UNITED NATIONS (AP) _ Vietnam and U.S. officials are considering arrangements for a joint excavation to search for Americans missing in action in an experiment that could be a breakthrough toward resolution of the MIA issue, officials said.

''In principle we are agreeable except in the crash sites where our security cannot permit foreigners to have access,'' Vo Dong Giang, a Cabinet minister without portfolio and the second-ranking official in the Foreign Ministry, told The Associated Press on Wednesday.

Other official American and Vietnamese sources said Vietnam has agreed to a U.S. proposal that the countries carry out a joint survey and excavation of a crash site near Hanoi as an experiment.

The date and other details are not worked out, the sources said.

U.S. excavation teams have never ventured into North Vietnam, although recovery operations were carried out in U.S.-backed South Vietnam before the fall of its capital, Saigon, in April 1975.

A State Department official in Washington confirmed that American officials have discussed the joint excavation of sites with a Vietnamese delegation led by Giang.

The official, who spoke on condition of anonymity, said the Vietnamese had agreed in principle to the proposal at meetings in Hanoi on Aug. 28-29 and in New York on Sept. 27 with Richard Childress, the National Security Councils's political and military affairs director.

The State Department official said that since both sides had agreed to speed up the search, the United States passed on to the Vietnamese ''many more cases'' at the meeting in Hanoi.

''Both sides are very positive about the process at this point,'' the official said.

The first official U.S. excavation in Communist territory was carried out last February in southern Laos at the site where a C-130 transport was shot down in December 1972.

Hanoi previously has limited American teams to rare visits of crash sites.

In his interview with the AP, Giang disclosed for the first time details of Vietnam's plan designed to settle the MIA issue within two years:

-The Vietnamese will do the major part of the searches.

-When it is difficult to reach crash sites, such as those in deep water or in an abyss where cranes and other heavy equipment would be needed, Hanoi would ask for U.S. help. ''These are few in number,'' Giang said.

-Giang said his government was agreeable to joint excavations. ''That was the talk in principle,'' he said, ''but in reality in my discussions with Mr. Childress, I ask him what specific cases might involve joint excavations because I couldn't imagine those cases. Mr. Childress has not explained that to me.''

A Pentagon official said that he thought the first such excavation would be at the site of a B52 bomber crash, but said he understood the project was still in the discussion stage.

U.S. and Vietnamese officials have agreed to another meeting, possibly a high-level one, to discuss Hanoi's plan, but no specific arrangements have been made, the State Department official said.

The stage apparently was set for the excavation in July, when U.S. officers who deal with MIAs conducted a preliminary site survey to determine how much manpower and equipment would be needed and the cost.

Giang said he agreed with the State Department that the talks were the most positive step in more than four years of trying to account for the 2,455 U.S. servicemen and civilians still listed as missing or unaccounted for in Southeast Asia, including 1,811 in Vietnam.

Vietnam has turned over the remains of 108 Americans, according to Pentagon records.

Giang said he had received information at the United Nations on six or seven new MIA cases, adding that they needed to be verified.

''I'm not sure whether they are American remains,'' he said.

Giang said the latest developments did not represent a shift in Vietnam's attitude.

''I think the reason there was such progress was the more favorable conditions in Vietnam,'' he said. ''In recent years we have less difficulties. That has permitted us to mobilize to a greater extent cooperation from the people in the search for MIAs.''

He said food production problems still remain but are less serious than five years ago. ''We are now just between the line of relative adequacy and insufficiency,'' he said.

He said better security has lessened the restrictions on search teams. Regional tensions also have been reduced through talks between the Communist Indochina countries of Vietnam, Cambodia and Laos, represented by Hanoi, and the non-communist Southeast Asian nations, represented by Indonesia, he said.

Vietnam is seeking to establish diplomatic relations with the United States in hopes of acquiring foreign aid and technical and management expertise. Its major benefactor now is the Soviet Union.

The United States' position is that Hanoi must first give a substantial accounting of all MIAs and withdraw its troops from neighboring Cambodia.

Giang said the timetable for withdrawal is now 1990 or sooner if a political settlement is reached. A year ago the Vietnamese were saying their troops would be withdrawn in five to 10 years.