The thing I remember about the day I came back from Vietnam was that the stewardess on the plane tried to cheer us up a little and she cheered over the loud-speaker, and there was absolute dead silence in the plane. And all of us had just returned. And I think that indicated that we didn't know what to expect.

SO SPOKE a Vietnam veteran on last night's ABC television documentary, "The Class That Went to War." The program focused with great force on the class that graduated from Chatham (N.J.) High School in 1964 - what happened to some of its 20 young men who went to Vietnam, the thoughts of some of those who chose not to go, the treatment received by the returning veterans, the feelings of a mother whose son was killed and a father whose son returned, and how Congress and the federal government are dealing with the rights and demands of Vietnam veterans.

The message of the program - that Vietnam was a different war from our earlier wars and that, as the documentary states, "the end of the war was only the beginning of [the veterans'] problems" - doesn't seem to be that hard to grasp. And yet the Carter administration and a majority of Congress still don't seem able to grasp it fully - or at least not nearly as fully as those at ABC who put together the documentary.

From the record this year, it doesn't appear that either the Carter administration or many in Congress are especially committed to dealing in strong ways with the unfinished business of the war. It was regrettable that the President signed the new GI Bill legislation the other day without using the occasion to mention the bill's weaknesses or pledging himself to work to correct them. The month before, Mr. Carter backed away from his own views on upgrading "bad paper" discharges by signing a narrow and vindictive piece of legislation. On top of this are the persistent problems of high unemployment among Vietnam veterans - despite the administration's gradly announced jobs program - and the uncertainties about the future role of Veterans Administration hospitals.

One of the fears of many veterans - those who spoke in "The Class That Went to War," as well as many others around the country - is that as time wears on they will increasingly be forgotten and that administrative or legislative solutions to their problems will not be forthcoming in meaningful ways. Ron Kovic, whose war wounds left him paralyzed from the waist down, put it this way: "We definitely felt betrayed by the government, and lied to and manipulated and angry, and absolutely fed up."

Those comments, along with the others, paint a picture that many will find too disturbing to think about. But the documentary is evidence of what may actually be a growing awareness that a much greater effort still needs to be made to ease the pains suffered by so many veterans.

We can think of other recent contributions, if anybody is interested in a reading list: "Dispatches" by Michael Herr, "A Rumor of War" by Philip Caputo, "Winners and Losers" by Gloria Emerson and Ron Kovic's "Born on the Fourth of July."

The President has acknowledged "a special debt of gratitude" to Vietnam veterans. Perhaps the books and documentaries - and a number of movies dealing sympathetically with the subject that are said to be on the way - can help illustrate the need for much more to be done by the administration and Congress to discharge that debt.