IT WAS ALL gall and wormwood for the Democrats Wednesday night, and nothing made them more bitter than the latest defection of Les Aspin, chairman of the House Armed Services Committee.

Aspin had once again made himself the center of attention, which in the opinion of his furious liberal colleagues is all he has in mind in his corkscrew progress towards a goal none of them can figure out.

Aspin voted with the Republicans on the bipartisan compromise that gives the contras military funds right now. He helped them beat back an amendment offered by Rep. Michael Barnes (D-Md.) that would have required the contras to account for the $27 million they got last year before they get any more. Aspin voted against the only amendment the Democrats wrested from the rout, a modest restriction on U.S. troop movements in the region offered by Rep. Robert Mrazek (D-N.Y.)

But the most grating sight for his colleagues, especially the Speaker, was Les Aspin standing on the Republican side of the chamber, jovially inserting his voting card, surrounded by laughing, chatting Republicans. They, of course, were so exhilarated by the fall of the Democratic fortress that they seemed totally unaware that they were kicking aside their own tradition of being cautious about wars and strict about money.

They were ecstatic in their march to folly in lockstep with their beloved president. Aspin's presence as a comrade in arms made them even happier.

Aspin had voted with his party in March, when they beat back contra aid. This time, building the suspense, he said nothing. But when the president quoted him in his last-minute Tuesday television appeal, his colleagues became suspicious. The president noted that Aspin had brought back from Nicaragua the welcome word that the peasants he talked to were all for contra aid.

A colleague said, "Right then I wondered what kind of a deal Les had made with the White House."

What makes it maddening for the liberals and moderates, who once thought Aspin was one of them, is that Aspin didn't have to do it. They regret the pro-contra votes of other Democrats, such as House Foreign Affairs Committee chairman Dante Fascell, but they understand it. Fascell comes from Florida. Jim Jones of Oklahoma deserted, but he's running for the Senate in a region where the fear of a Sandinista invasion, as nurtured by the president, is a political factor.

But Aspin comes from Wisconsin, which, like most of the country, is anti-war. He has no serious opposition. He could hardly have more power in his present position. Generals bow and scrape to him and he flies on Air Force jets, with colonels smoothing every inch of his path. This is heady stuff for a man who once worked as a civilian "whiz kid" at the Pentagon. But Aspin wants more, and nobody is sure what it is, except to play games and keep his colleagues guessing.

He has been told all this to his face. At a Democratic caucus on the MX, he was accused of selling out on that issue. He got his chairmanship by assuring liberals and moderates he would join them in downing the "Peacekeeper," but he ended up leading the fight to keep it alive. Last year, on the military budget, he abandoned the House position for a $10 billion cut and was called on the carpet in a showdown in the Speaker's office. In its heated course, Rep. Marty Russo (D-Ill.) shouted at him, "Some time, Les, you have to take a stand."

Aspin appears unrepentant. "It just bounces off him," said an observer.

By ten o'clock Wednesday night, Democratic disappointment had turned into rumblings of insurrection.

Liberal and moderate Democrats were promising each other they would turn him out of the chairmanship.

Rep. Barbara Boxer (D-Calif.), a member of Armed Services, said she was "stunned" by Aspin's performance. "Someone who is that far out of sync with the (Democratic) caucus doesn't belong in a position of leadership," she said. "He has not only left us, he has stomped on us."

Plotting revenge on Aspin was the only wretched diversion in the long night of disaster. Realists were dubious. An alternative must be found and unity achieved. Rep. Charles Bennett (D-Fla.) was good on MX, but bad on contras. Nick Mavroulis (D-Mass.) is a possibility, but consensus in a committee that is dominated by hawks is hard to achieve.

The morning after, Speaker O'Neill, sitting in the ashes of the worst defeat he has suffered at the hands of Ronald Reagan, was asked if Aspin could be dislodged.

"I won't be here," he said heavily. "But I wouldn't vote for him; I didn't vote for him the first time, and it turned out just the way I thought it would. He has broken his word to a lot of people out there."

Mary McGrory is a Washington Post columnist.