A U.S. delegation is preparing to travel to Vietnam later this month to discuss one of the more stubborn issues between the two countries--the fate of the American missing in action.

The group, to be led by Richard C. Armitage, deputy assistant secretary of defense for East Asia and Pacific in the office of international security affairs, will be going against a backdrop of international concern that the adamant stands of the two countries on political issues involving the regions are fueling tensions there.

Armitage will be the highest ranking official in the Reagan administration to visit Vietnam. The group, which is to be in Hanoi Feb. 23 and 24, will include representatives of the State Department, but U.S. officials insisted yesterday that the agenda will be confined to the MIA question.

The most outstanding political difference between the two is the Vietnamese military presence in Cambodia.

Last fall Hanoi permitted a private group of four American veterans of the Vietnam War to visit there to discuss the missing in action and Agent Orange, the chemical used as a defoliant by U.S. forces during the war, and which some have charged with having toxic effects on people. The veterans emerged saying Vietnam was prepared to assist other private citizens trace missing servicemen or investigate the effects of Agent Orange.

Pentagon officials at that time reportedly expressed fears that Vietnam wanted to turn the MIA question into something of a political show. Sources say they have been pressing for a high-level U.S. delegation to be sent there to revive the official channels that have functioned since the Communists' 1975 victory in Vietnam for questions about the MIAs and the recovery of bodies of American servicemen.

U.S. officials say that 2,500 servicemen are still being carried as missing in action in Vietnam, Laos and Cambodia. Of those, officials say, about 50 are reliably known to have been captured alive. The Vietnamese insist that they have done everything possible on the corpses of the missing servicemen. Agence France-Presse reported from Hanoi yesterday that a Vietnamese source there said 585 American prisoners and 74 corpses of American servicemen had been turned over to U.S. authorities, with the most recent transfer occurring last July 7.

There has been speculation that some officials within the Vietnamese leadership have been arguing that the country must take a more conciliatory stance if it is ever to see an end to the almost four decades of deprivation it has endured during the communist struggle for power. Sources say the willingness to admit the U.S. group at this time may be a move in this direction. There are those, however, who say the visit could also fall in line with Hanoi's contention that the U.S. campaign to put Vietnam in political and economic isolation is a failure since it demonstrates that the architect of that policy has to deal with it.

Observers here take at face value the official U.S. contention that the talks will be limited to the missing in action question and will not go into political questions. It would be in keeping with the administration pledge to do all it can about missing servicemen without, however, giving way on the insistence that Hanoi must pull out of Cambodia.

While the United States, in a policy that goes back to the Carter administration, has taken the lead in trying to put Vietnam in isolation, Washington's Southeast Asian allies have fought successfully each year in the United Nations' General Assembly to deny the Cambodian seat there to the government Vietnamese troops installed in Phnom Penh when they swept into the country in December 1978.

Vietnam has refused to bow to demands that it pull its forces out of Cambodia, insisting that it must first have some kind of security guarantee against what it terms the "Chinese threat." China, which had been the Khmer Rouge's closest ally, invaded Vietnam in early 1979 to "punish" Hanoi for the attack into Cambodia.