HO CHI MINH CITY, VIETNAM -- America has left a powerful legacy here. Some of it is realistic, some exaggerated, but all of it is being preserved to fuel two seemingly contradictory Vietnamese preoccupations.

One is to keep fresh the memory and human cost of the war with the United States. The other is a strong desire, 12 years after that war's end, to normalize relations with the United States and receive American aid.

Where the two themes meet is Vietnam's belief that the United States should pay for what Hanoi's leaders call its past "war crimes" through large-scale aid.

A decade ago, Vietnam's demand for U.S. aid helped scuttle an effort by the Carter administration to restore relations. The Vietnamese have not said much about it since then. But now, the issue is being subtly raised again by new leaders attempting to reform their country's economy.

The link with the past is preserved in the display here at the "American War Crimes Museum" of an impressive collection of U.S. military hardware with labels reflecting Hanoi's view of the decade-long war.

Beneath a 175-mm howitzer gun, a sign tells visitors: "The U.S. imperialists mostly used this howitzer in their numerous criminal acts in the Iron Triangle area." An M113 flame thrower is described as "used in burning villages of the South Vietnamese countryside."

Inside the museum are photographic memorials to what the Vietnamese refer to as "atrocities of the U.S. imperialists," including photographs of the massacre of villagers at My Lai.

To an American, the often-macabre recital of "atrocities by U.S. imperialists" may seem trying or highly one-sided in its historical accuracy. Any suggestion of killings of civilians by the Communist side are routinely dismissed as "propaganda." Rarely is mention made here of the South Vietnamese Army as having played any role in the conflict.

Yet, however open it may be to debate among Americans, Vietnam's version of the Vietnam War -- in the monuments, the constant references to "atrocities" in Vietnamese-made films about the war -- illustrates the depth of emotions that persist and the still perceptible "wounds of war," as foreign minister Nguyen Co Thach put it.

Much of the legacy of America's involvement here is less subjective. There are still countless thousands of Amerasian children -- fathered by GIs -- left behind in the south, who have grown into young adults.

Also, western and Vietnamese health officials are still trying to determine the health effects of the spraying of the defoliant known as Agent Orange by the Americans. Dr. Arnold Schecter, a New York physician working with the Vietnamese on the Agent Orange question, said persons tested in south Vietnam show higher levels of the potentially cancer-causing dioxin found in Agent Orange than the average person in the United States and Europe and that further study is needed. The Vietnamese, without statistical proof, blame a higher-than-average number of deformed babies on the wartime use of the defoliant.

It is this collective legacy, as Vietnam sees it, that lies at the heart of Hanoi's insistence that the United States should pay for past "crimes" through massive monetary aid.

But Vietnam's view is not shared by official policy makers in Washington, for whom the only continued interest in Vietnam is the emotional issue of the 1,800 servicemen still missing from the war.

The differing perceptions threaten to collide, as the two sides prepare to resume talks over "humanitarian issues" that Hanoi hopes might pave the way for eventually normalized relations.

It has happened before. Vietnam's demand for U.S. aid a decade ago was a major impediment to the normalization of relations attempted during the Carter administration.

No one here specifically uses the term "reparations." But the feeling is unmistakable: the Vietnamese want American reconstruction aid and feel they deserve it.

During the past few months, as Washington-Hanoi talks have resumed -- with President Reagan naming a retired chairman of the Joint Chiefs of Staff as his personal emissary -- the Vietnamese appear once again to be raising subtly the dormant issue of America's financial "obligation" to Vietnam.

Thach, interviewed during a recent trip here, raised the problems of Vietnam's many "victims of war" and said that if the Americans expected Hanoi's help in accounting for missing U.S. servicemen, "then the Americans can help us on our wounds."

Thach said he was sharply criticized by his colleagues at the Sixth Communist Party Congress in December for cooperating with the United States on the MIA issue and not having received anything in return.

At a luncheon with a visiting American journalist in Hai Hung Province near Hanoi, a local Communist Party official asked continuously about the reasons for the U.S. government's reluctance to "pay" for its past actions.

Bui Tin, a high-ranking journalist for the Communist Party daily newspaper Nhan Dan, began another interview by listing American "crimes."

"Twelve million tons of explosives were dropped," he said. "One-third of our forests were fully destroyed. Hundreds of towns, roads and bridges were destroyed. It's a little bit surprising that the Vietnamese don't show more hatred toward Americans."

"We are eager to turn a new page in relations between Vietnam and the United States," he said. "So the Americans should show their friendly hand toward Vietnam -- it would be a great sign."

Officially, the American government has said that there can be no talk of normalization until the question of missing U.S. servicemen is resolved, and American officials have repeatedly resisted Vietnam's efforts to link that question to broader political issues, such as future U.S. aid.

Vietnam recently agreed to meet with Reagan's envoy, retired Gen. John Vessey, to discuss the MIAs, but Thach said Vietnam will use the meeting to raise other "humanitarian issues."

Statements from Washington indicate that Vessey's mandate from the president would not allow him to discuss larger questions of aid and normalization.

Even assuming the MIA issue were settled, U.S. officials have repeatedly said that there would be no normalization until after Vietnam has withdrawn its troops from neighboring Cambodia, which it invaded in 1978 and continues to occupy.

Secretary of State George P. Shultz repeated that stand in Singapore last month, telling America's Southeast Asian allies, "We will not move toward normalizing relations with Hanoi until a settlement has been reached . . . which involves the withdrawal of Vietnamese forces from Cambodia."

But even if the MIA question were resolved and Vietnam had withdrawn its troops from Cambodia -- Hanoi has said repeatedly it will do so in 1990 -- the prospects for any substantial American aid would remain slim.

"If the Vietnamese think we're going to rush in there with aid, they're out of touch with reality," one American official said recently. "Foreign aid is a dirty word in Washington right now. We can't even get more aid for our friends."

This official said that what the Vietnamese fail to understand is that, since the fall of Saigon, "Vietnam's intrinsic importance to the United States is zilch, zero. Vietnam's only importance to the United States is the effect it has on its neighbors. Our primary national interest in this region is with Thailand and with ASEAN," the six-country non-communist Association of Southeast Asian Nations.

Although that view is not officially expressed U.S. policy, it represents a large if not dominant sentiment among American policy makers and other Vietnam specialists debating the policy Washington should adopt toward Hanoi.

According to this sentiment, even the issue of missing Americans, which Hanoi has seized upon as its only bargaining chip with the United States, may become less potent if a new administration in Washington in 1989 pursues it with less zeal.

There is, however, another, somewhat opposing view: that Vietnam, in the middle of an economic reform program predicated on an opening to the West, could potentially be lured away from its reliance on the Soviet Union, its principal military ally and foreign aid supplier. Moscow currently provides about $2 billion a year in aid.

According to this view, the United States could turn Vietnam at least toward the West by dropping its preconditions, normalizing relations and becoming involved in trying to help shape the country's development. By recognizing Hanoi and becoming involved here, this view holds, the United States would be in a better position to influence Vietnam in other areas more critical to American interests, such as Vietnam's foreign policy in the region.

"It is difficult to believe that because of the MIAs you permit yourself to leave a big important country completely white on your map and in a very important region," one Western European diplomat said in Hanoi. "If Ronald Reagan really wanted to do something politically interesting in his final year, he would show that the United States is big enough to make amends with a former enemy and in the process make the United States operational in this region once again."

Proponents of this view note that the Vietmanese, despite their constant references to "American imperialism" and past "atrocities," actually harbor more resentment toward the Soviets than they do toward the Americans. Reports from recent travelers seem to support this view. The Vietnamese in the north and the south seem genuinely friendly toward Americans.

The Soviets are believed to have several thousand advisers and technicians in Vietnam.

Thach, in the interview, suggested that Vietnam would not mind "diversifying" its aid source away from the Soviets. "Diversification is a good thing," he said.

Most analysts agreed, however, that even if Hanoi resumes some level of ties with Washington, Vietnam is unlikely to end its close ties to the Soviet Union any time soon. The level of Soviet aid, they said, is greater than any western country would be willing to match.

Some observers here and in Bangkok noted one important factor that could force the United States to become more engaged in Vietnam, even if there is an intrinsic desire to close the door on Indochina. That factor is a large immigrant Vietnamese population now living in the United States, which could potentially form a powerful lobby for closer ties with the government in Hanoi.

As Vietnam loosens its policies toward overseas Vietnamese, more of them will be coming here to visit. Increasing traffic may require the United States to open an interest section or consular office here, drawing the United States back into Indochina, whether U.S. policy makers like it or not.