Among the few happy Democrats hereabouts is Rep. Les Aspin (Wis.), who has been "punished" for his defection on a major party issue by being elected chairman of the House Armed Services Committee.

The gawky, talky, one-time Pentagon whiz kid was put over with a hand from liberals who have spent much of the past two years calling him a "sellout" for his critical support of President Reagan in saving the MX missile.

Aspin's triumph is seen in various ways: as a crushing defeat for House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who made a dramatic plea for the incumbent and the seniority system; or as a Yuppie revolt led by those who at heart care more about the process than the issues and who could not face another two years of 80-year-old Rep. Melvin Price (D-Ill.) as their televised spokesman on the great questions of war and peace.

Their rationalization is that Aspin, who defied the majority to embrace the curious formulation of the president's Scowcroft commission that the MX is a lemon but a necessary expression of the "national will," is about to change his spots again and oppose the missile.

"Obviously, this was something I had to wrestle with," said Rep. Barney Frank (D-Mass.), "but my strong sense, from political logic and some conversation, is that he will be against it. Now that he is chairman, Les will feel institutional pressure to represent the Democratic Caucus position against MX. And, of course, we are now in the negotiating mode with the Soviets."

Aspin tied his support for MX to arms control talks, arguing that the intercontinental missile is a "bargaining chip." Most recently he contended that the Soviets should not be "rewarded" for walking away from the bargaining table by "unilateral" cancellation of the $20 billion MX program.

Rep. Nicholas Mavroules (D-Mass.) thinks he has a stronger commitment from Aspin. "I feel he has no choice but to come out against MX," he said. "If he were to come out in opposition to it, it doesn't have a prayer."

Another liberal Democrat said he is sure that Aspin, who since his victory has issued muffled statements, "is just looking for a graceful way out."

Aspin knows that without his backing MX, which is on shaky ground in the Senate, is dead in the House. He also understands that without his pro-MX stand, he would not have had the support of the hawks who roost thickly in the Armed Services Committee. He undoubtedly understands the final irony of his victory: His left-wing critics had no choice.

Price was out of it. To elect the next in line, Rep. Charles E. Bennett (D-Fla.), was unappetizing. Bennett was, to be sure, an opponent of the MX, but "against us on everything else," as one liberal put it.

So Aspin has been rehabilitated as an articulate critic of the Pentagon who can slug it out, line by line, on the budget with Defense Secretary Caspar W. Weinberger. Aspin has been repainted as a critic of the Vietnam war -- although some older hands can remember him standing in the all-but-deserted headquarters of Lyndon B. Johnson during the 1968 Wisconsin primary plumping for the war-trapped president.

His criticism of the Pentagon is often peripheral. An indefatigable producer of news releases, he cornered NATO's then-commander, Gen. Alexander M. Haig Jr., for using the system to transport his dog.

But Aspin's susceptibility to being seduced into thinking himself a mover and shaker for arms control soured his colleagues, who see him less as a maverick than as an opportunist.

He seems to have been genuinely taken aback by the fury he generated with his MX support. He thought he had appeased the peace constituency by supporting a moratorium on tests of anti-satellite weapons. Aspin is a "defense intellectual" who schemes like a ward heeler, sacrificing consistency for political gains not immediately apparent to people who care all day every day about arms control progress.

MX is fading as a flash point for peace groups. It is being replaced by "Star Wars," Reagan's answer to arms control. Memories of Aspin's defection on MX will recede as Democrats begin to see the virtue of taking the arms race into space.

Star Wars is the gravest escalation since the decision to put multiple warheads on missiles. Already the leading candidate to succeed O'Neill as Speaker, Majority Leader James C. Wright Jr. (D-Tex.), has startled the White House with an effusive endorsement. He issued a "clarification," which basically said that he, like Aspin, is spooked by Reagan's program of arms control, which is to go on building nuclear "bargaining chips" while insisting that his only hope is to eliminate them.