IT IS EVEN HARDER for governments than for people to admit that they are wrong.

For an individual, saying "it was my fault" can sometimes close a question. But when a government says it made a mistake, it can open up questions -- and cost vast sums of money.

And that is why, to put it briefly, three years after Congress ordered the Veterans Administration to produce a study of the effects of Agent Orange, the toxic herbicide used as a defoliant in Vietnam, the study is nowhere in sight.

If the VA were to confirm the suspicions of Vietnam veterans who have experienced cancer, deformed children and stillbirths that Agent Orange is the villain, the government could be subject to claims that could drain the Treasury dry.

VA Administrator Robert P. Nimmo was blunt about it in testimony before the Senate Veterans Affairs Committee last year:

"We would be looking at hundreds of millions of dollars per year, going into the middle of the next century."

Obviously it was something that Washington should have thought about before it sprayed the jungles of Vietnam with 10.5 million gallons of Agent Orange from 1962 to 1971. It was stopped then because someone noticed that a large number of deformed babies was being born to Vietnamese women and decided that Agent Orange might have something to do with it.

Governments have a way of becoming infatuated with new weapons and rush pell-mell into using or testing them without regard for the malign consequences on their own people.

Twenty-four citizens of Utah are in court today trying to make the government admit that the atomic testing of the '50s and early '60s was bad for their health and that of their families.

It took the government 10 years to acknowledge that the toxic effects of Agent Orange had been brought home by many veterans -- but not that Agent Orange was the cause. It's victims, who did not know what ailed them, were treated, they say, like "nuisances" at VA hospitals by doctors who were accustomed to dealing with the simpler, starker cases of missing arms and legs or broken bones.

Ronald Reagan last year signed a bill making Vietnam veterans eligible for treatment of its awful symptoms, but specifying at the time that no extra funds were to be used for the purpose.

The "Atomic Veterans," those GIs who were marched close to Ground Zero after the 89 atomic tests that exploded in the deserts during the years of the government's first fine careless rapture with nuclear power, finally got the right to get VA treatment for the afflictions they subsequently suffered. It took them only 25 years.

Agent Orange is not only a fiscal hazard for the government. It is of the utmost touchiness politically.

The Reagan administration has been making a concerted effort to convince the world that the Soviets are using chemical warfare in Afghanistan and other contested areas of the world. To admit that we were guilty of a comparable practice in our long, futile struggle to win hearts and minds in Indochina would be, at the least, highly embarrassing.

So it is no wonder that the VA has not been in a hurry to finish -- or even start -- its work on Agent Orange. Obviously a definition of its causes and symptoms, the issuance of standard screening and treatment procedures, would help the veterans. It would, however, do nothing for the government's reputation or its budget. The VA cannot be said to be proceeding with even "deliberate speed." They can't promise a line of the study until 1988 or 1989.

"This is unacceptable, and I am outraged," says Rep. Tom Daschle (D.-S.D.), a Vietnam-era veteran himself and chairman of the informal Vietnam Veterans in Congress Caucus.

Daschle intends, before the session is over, to introduce legislation to take the Agent Orange study out of the limp hands of the VA and to turn it over to the Health and Human Services Department or the Communicable Disease Center, either of which, he hopes, might evince more interest in the medical, as opposed to the political and financial, aspects of the situation.

He also will propose compensation for those identified Agent Orange victims -- some 80,000 of them -- who suffer from "soft" cancers and recurring skin disease known as chloracne.

One of the witnesses at the hearings Daschle has held both here and in the West told of the pain that Washington stonewalling has caused Agent Orange casualties and those who try to help them. Phil Burgess, president of the Vietnam Veterans of Montana, put it this way:

"What do I do when a family comes in and they have a child with a missing arm? Where do I send them? To the veterans hospital? Where do these people go?"

The government's answer to these questions, so far, has been, "Don't ask me." It doesn't even have the grace to give the standard Vietnam dismissal, "Sorry about that."