THE WARMING between the United States and Vietnam this week brought to Washington Nguyen Co Thach, vice premier and foreign minister. He had seen Secretary of State Baker in New York. Here he met with, among others, retired Gen. John Vessey Jr., whom President Bush has named to tend the anguishing issue of the 1,700 Americans still listed as unaccounted for 15 years after the Vietnam War. The two reported "new levels of cooperation" in pursuing MIAs lost in Vietnam and Laos.

The Hanoi-Washington thaw began last summer, when the United States reversed course on the neuralgic issue of Cambodia and started treating Vietnam not simply as an antagonist supporting a puppet government in Phnom Penh but as a necessary partner in negotiating civil peace. The international, regional and Cambodian actors are now engaged in testing this approach. Progress achieved so far has brought Vietnam close to satisfying the principal American condition -- a Cambodian settlement -- for normalizing ties and ending its punishing economic isolation. But as it must, Washington continues to declare that the "pace and scope" of normalization hinges on Vietnam's cooperation on MIAs.

The Vietnamese have their own sources of bitterness toward the United States. But no aspect of Vietnam's conduct has produced more bitterness among Americans than its toying with the MIA/POW issue over the years. At first it seemed (and to some it still does) that Hanoi was playing this card against delivery on American pledges of reconstruction aid -- pledges that Washington considered voided by Vietnamese violations of the Paris peace accords. Then it seemed the issue was caught up in internal Vietnamese wrangling. Information and remains have come out painfully slowly and incompletely, gratifying and frustrating Americans at the same time. Questions linger about whether some live Americans remain behind -- Vietnam denies it. Would it help, as some suggest, to devise categories of "unregistered" POWs or "deserters" to skirt Hanoi's insistence that no American "prisoners" remain "under its control"?

Vietnam should understand that a great number of Americans, across the political spectrum, will be watching to see how fully and promptly it makes good on its latest MIA vows.