I ONCE -- brace yourself -- appeared in a movie. The film was called "The Seduction of Joe Tynan" and my cameo appearance came about because I was, besides stunning, the consultant on the script. I was the one, history will record, who told Universal Studios that most senators are not driven around in limousines. Nowadays, they could hardly afford the gas anyway.

This is something the Congress is not likely to admit. It is loath to say that things are rough, even in Washington, and that the Congress -- not to mention the senior civil service and the judiciary -- could use a raise. All Congress has to do is to vote one. All it needs is the guts.

Congress feels, though, that the voters consider all governmental pay raises ill-begotten, and so legislation to raise pay always comes up at the end of the session, as if it were an afterthought. Even then, the ruse doesn't usually work. The legislation is either ducked entirely or rejected on a (unrecorded) voice vote. What is recorded are sentiments of the sort expressed by Barry Goldwater, who observed at the end of the last session that if he voted for a pay increase he would not be able to return home to Arizona. His constituents would kill him.

Notice that he did not say that he and his colleagues did not deserve a raise. He did not say that the senior civil service, some 34,000 top-level employes whose salareis are linked to those of members of Congress, also didn't deserve a raise and he said nothing about federal judges, cabinet officers and Supreme Court justices. All of them have their salaries set by Congress. When congressional salaries go up, theirs do too.

The reason Goldwater and his colleagues do not question the need (as opposed to the political wisdom) of a raise, is because the need is unquestioned. Before the Supreme Court recently permitted a 16.8 jpercent increase in judicial salaries, a federal district judge was paid $54,500 a year. That is nowhere near what a lawyer could make by shuffling papers, mumbling about the party of the first part, and taking long lunches. But what a judge could make as a lawyer is the least of it.

It is what a judge used to be able to make as a judge that really matters. A lawyer who became a judge in 1968 was paid $40,000. Had his salary kept up with inflation, he would have made $110,000 a year by 1980. But it didn't keep up.Instead, he made $54,500 -- a significant erosion of his standard of living. The same principle holds true for the Supreme Court, the cabinet, the senior civil service and the Congress itself. All of them have received what Congress has had the guts to give itself -- next to nothing. The result has been an exodus of experienced people from the civil service and even some from the judiciary.

But an equally serious, or maybe more serious, result has to be the inexcapable conclusion that Congress simply lacks the nerve to do the right thing. It would be one thing if Congress thought the judiciary and the senior civil service were grossly over-paid, but that is not the case. In fact, not only does common sense say otherwise, but a succession of study commissions have recommended raises -- some of them so fat as to make federal service downright attractive.

All of this would not matter much if we were talking only of congressional salaries. And it probably wouldn't even matter if we were talking just of salaries -- anyone's. But what is really at issue here is what is sometimes called Doing The Right Thing, doing what must be done regardless of popularity.

It is here that Congress blatently and with much publicity, candor and admissions of weakness, flunks the test. It is, it admits, simply not up to the challenge and if it does so poorly here, why should we expect it to do any better when it comes time to face the harder issues, the ones that are bound to arise in the upcoming era of scarcity and high energy costs.

The irony is that Congress has played chicken with the pay issue to protect its image, to cover itself and seemingly endear itself to the voters. In doing that, it has simply proved that when push comes to shove, it will do what is popular, rather than what is right. As a result, it doesn't appear principled or frugal, but merely timid -- worth every cent it's getting.