Les Aspin's office is a cluttered warren of political activity. It is chopped in half by a partition shielding a corps of unpaid interns who dispatch a million pieces of mail a year to voters and reporters in Wisconsin. On a ledge behind Aspin's desk stands a ragged row of open manila files, his reference library on defense and arms control issues. On the opposite wall, where the awards and handshake photos should hang, Aspin has mounted a green chalkboard large enough for a friendly seminar.

"We'll put some numbers up and fool around with it," says the former economics professor, now the chairman of the House Armed Services Committee. He waves casually at columns of figures on the green board that show projected deficit reductions through 1987. Then he slips on a blue baseball cap emblazoned "Peacekeeper Flight Team," sent to him by friends in the White House as a souvenir of the MX missile funding battle in Congress two months ago. Aspin picks up another souvenir, a foot- long skyrocket in the shape of an MX.

"Do you suppose this thing works? It has a fuse. I guess you just light it. I think I'll send it to Mary McGrory," he says jokingly.

Washington Post columnist McGrory was among many who were outraged by Aspin's unexpected support of President Reagan's request for 21 new MX missiles. Aspin argued the missiles would be a "bargaining chip" in reopened arms control talks with the Soviet Union. But some congressional colleagues accused him of welshing on commitments to oppose the missile, commitments they say he made during hs marathon campaign for the Armed Services Committee chairmanship. Columnist McGrory accused Aspin of "slithering on the MX."

"It's a sign of the liberal bias of the press that if the liberals are unhappy with me, that must make me really miserable, whereas if the conservatives are unhappy, that somehow doesn't matter, because they don't really count," Aspin said. "But if liberals are unhappy, you know, all the bells go off."

"He's genuinely an independent thinker," said Maureen Shea, his former wife. "People get dismayed when they try always to put him in a liberal category. He's his own man."

Rep. Howard Wolpe (D-Mich.) was among those who felt "betrayed" by Aspin after the MX vote. "He would not now be chairman except for the votes of a lot of us who believed he would vote against MX," Wolpe said. "Les sat down beside me in the Democratic Caucus and said he was opposing MX, and that his position was consistent with favoring it last year. I said I didn't care for his logic, just or his position."

"I leaned across Howard and listened," remembered Rep. Robert Edgar (D-Pa.). "He misled Howard."

Aspin said he does not remember the conversation with Wolpe and Edgar. Did he mislead anyone? "No. I mean, obviously I did mislead some people, but I did not try to mislead people," he said.

"I'm a very disillusioned friend," said Rep. Les AuCoin (D-Ore.). "I hope it's redeemable, otherwise I'll fight the guy right to the end."

Aspin said such remarks are like "water off a duck's back," a cheerful response embodying the economist's trust in logical deduction, the politician's faith in his own views, the intellectual's fascination with nuclear strategy and the maverick's delight in thumbing his nose at the prevailing view.

"It's an intellectual proc "Once I've thought it through and come to a conclusion, I don't care what people think. I'm very comfortable with where I'm at." WHERE ASPIN is at might be called the political catbird seat of defense policy. In January, he mounted a coup that unseated Rep. Melvin Price (D-Ill.), the aging and ailing chairman of the House Armed Services Committee. After making more than 700 calls to fellow Democrats scattered about the country during the Christmas break, Aspin had gained enough support to leapfrog five Democrats above him on the seniority ladder. At 46, Aspin had become a key congressional player in the shaping of the Pentagon's $300 billion budget, an amount greater than the gross national products of all but a handful of countries.

Aspin's new role gives long-term comfort to his

considerable ambitions. When a constituent recently asked Aspin where

the congressman hoped to be in 20 years, he replied without hesitation: "Chairman of the House Armed Services Committee."

Past committee chairmen -- and many members -- had a history of uniformed service in World War II. Their role on Armed Services often seemed to be a protective extension of the patriotic team they served during the best years of their youth. Most also had major defense installations on their home turf. Aspin has no military bases or significant defense payrolls to protect in his district; his war was Vietnam; he served not in the trenches, but as a cost-effectiveness expert at the Pentagon, one of former defense secretary Robert McNamara's "whiz kids."

Alain Enthoven, who was their immediate supervisor, recalled recently that the whiz kids in the military often wore civvies to the office. "I did not encourage them to wear their uniforms every day because I wanted to encourage the kind of independent thinking of a civilian agency," Enthoven said.

Aspin's independent thinking may bring significant changes to the huge American military machine. From his high-backed chairman's seat in the Armed Services Committee hearing room, he will cast an economist's eye on the defense department's annual wish lists. "It's a matter of point of view," said Enthoven, now a professor at Stanford University. "The economist thinks ends and means. The military man says: battleships. The economist asks: 'What are these battleships for? What is the end? Is this the best means, and most cost-effective, for this end?'

Aspin's vision of his committee's role goes well beyond the cutting up of the annual Pentagon money pie. Through a newly formed Defense Policy Panel he hopes to examine the department's decision-making system, the roles of the service secretaries, and the influence of top field commanders.

"Until now," says Warren Nelson, Aspin's chief defense aide, "the committee has dealt with the final hairs on the tip end of the dog's tail. Now we want to get into the dog's brain."

Reform of the Joint Chiefs of Staff is high on Aspin's list of targets. The chiefs are "a bureaucracy that can't make decisions," he said, " . . . bogged down in the need for unanimity." The chiefs' loyalties to their own military branches make the chairman a victim of interservice rivalry -- "The chairman of the joint chiefs is a eunuch," he said. Aspin's proposal would empower the chairman of the joint chiefs to function more like a corporation chairman overseeing the chief operating officers of his subsidiaries. This approach, an Aspin staffer says, has Army and Air Force backing, as well as support in Congress, but it is opposed by the traditionally separatist Navy and by Secretary of Defense Caspar Weinberger, who feels the present arrangement works well.

Other significant items on Aspin's reform agenda include:

*Cutting the pensions of future military retirees. Aspin has devised a legislative tactic that would force the Defense Department itself to chop $4 billion off the $18.2 billion retirement program.

*Trimming large chunks off the administration's $3.7 billion budget request for research into the "Star Wars" strategic defense initiative.

*Levying fines on defense contractors who overcharge, do bad work or claim unallowable expenses. Under present law, such contractors are usually required only to refund money or redo work.

*Toughening up the "revolving door" arrangements that enable people to shuttle back and forth

Continued on page 22 between military and civilian jobs in the Defense Department and posts with contractors.

*Increasing competition among defense contractors by abolishing the all-or-noth bidding system which awards an entire contract to a single manufacturer.

*Creating what one Armed Service Committee aide called "a system of rewards and punishments" to discourage such costly duplications as the three different close air support systems now operated by the Army, Air Force and Marine Corps.

Aspin says he hopes to bring together the doves and the hawks on his committee toward the "common-sense middle." He wants to unite "the people who are against the weapons systems and against the nonsense in the defense budget" with those who "are for the weapons systems but tend to be for all the nonsense, too."

Says Aspin: "The trick is to be for the right stuff and try to do something about the wrong stuff. What you find is people who are for the MX and military retirement. And people who are against both."

LES ASPIN is 6 feet 2 inches tall with prematurely silver hair and a tonsure-like bald spot. He is alternately charming and inconsiderate, a windmill of arms and shoulders when he speaks, a bluster of energy and goals and four-letter words. A former Rhodes Scholar with a PhD from MIT, he is a serious thinker who also loves political pit fights.

Aspin clearly enjoys the independence of an unmarried man with a $75,100 congressional salary. He buzzes around Washington in a Renault Fuego sports car -- the French carmaker has a controlling interest in American Motors Corp., a major manufacturer in his district. Divorced since 1979, he is rarely without a date on his frequent excursions to political receptions, Kennedy Center events and plays at Arena Stage and the Folger Shake- speare Theatre. He once shared his small Georgetown house with Judith Miller, a New York Times correspondent now based in Egypt. Today he is often seen with Karen Sughrue, executive producer of CBS' "Face the Nation."

As driven in recreation as he is in politics, Aspin fights a bulging wasitline with an aggressive game of wintertime squash. "He's combative, but he needs to get his wind better," teases playing partner Rep. Sander Levin (D- Mich.). In summer he curses missed tennis shots at the St. Albans Tennis Club and sails competitively on Lake Beulah in Wisconsin.

Aspin also follows spectator sports, particularly if teams from his native Milwaukee are involved. The night after the MX vote in the House of Representatives, he left Capitol Hill so quickly that the White House failed in four attempts to reach him. Finally, his administrative assistant, Penny Gentilly, remembered the Milwaukee Bucks were in town at the Capital Centre. "Maybe you can reach him there," she told the caller. "Oh, I wouldn't want to interrupt," replied President Reagan. "Just tell him I wanted to thank him from the bottom of my heart." AS HE ROAMS the Democratic aisle of the House chamber, Aspin's suit hangs on his large frame like a loose sack. He tilts his round head and gets right up in the face of whomever he's massaging on the vote of the moment. When he plops in a heap into a wide armchair, he lifts his scuffed shoes up on the seatback in front of him. Hands folded beneath his chin, he resembles a grad student in perpetual seminar. Which, in a way, he is.

Aspin is a defense intellectual, a member of an elite fraternity of experts on strategic weaponry, arms control, Soviet military strength and the arcana of the American defense system. His brethren are scattered across the country in think tanks and universities. They float in and out page 23 of official positions and include people such as James Woolsey, undersecretary of the Navy in the Carter administration; Leslie Gelb, who was assistant secretary of state under Carter; Will Taft, assistant secretary of defense under Caspar Weinberger.

"Les' idea of a good time," says one longtime Aspin- watcher, "is a three-day seminar on arms control at the Aspen Institute in Colorado."

Aspin may be Congress' only in-House academic who studies the institution at the same time he participates in it. When not in the midst of a policy battle, Aspin turns out articles and papers at a rate that would make most professors blush. His 1975 analysis in Daedalus, the journal of the American Academy of Arts and Sciences, is cited for its insights about the political process. "Les showed that Congress will never decide anything on substantive grounds if it can decide it on procedural grounds," said Graham Allison, dean of the Kennedy School of Government at Harvard.

Aspin's life in the world of defense intellectuals sometimes takes the form of a small dinner party at his home, which one guest described as "bearing less resemblance to a Georgetown salon than to a college dorm with posters on the wall." Aspin uses the same caterer and serves the same menu at nearly every party: chicken creole, rice, snow peas and baked Alaska. "I just call the caterer and tell him, 'The usual,' Aspin's secretary. "He already has a key to the house."

Aspin is a sought-after guest at the dinner tables of Washington's political and journalistic elite. But he is notorious for clumsy manners. "Les doesn't have much small talk," said one amused Georgetown hostess who has watched the energetic legislator fall asleep during dinner when the conversation strayed too far from weighty issues. "Les can be charming," says a journalist who has shared several dinner tables with him. "But he's socially oblivious . . . One time a big silver bowl of ice cream was being passed around for dessert, so the guests could serve themselves. When it got to Les, he just started eating right out of the bowl. After a while, he passed it on."

Aspin has other quirks, too. Every day he brings an exuberant mongrel sheep dog named Junket to his office in the fourth floor of the Cannon Office Building. She nuzzles and licks visitors. When Defense Secretary Weinberger paid Aspin a courtesy call soon after he became committee chairman, the first thing the rumpled representative said to the strait-laced cabinet member was, "Cap, I want you to meet my dog, Junket." Junket happily licked Weinberger.

When Aspin's staff inquired if his chairmanship finally meant a move to larger quarters near the committee rooms in the Rayburn Building, Aspin said: "No way. Junket would get lost. She knows her way to this office."

Aspin is a hard worker whose charm derives from what Karen Sughrue calls "an incredible zest for life and whatever he's doing at the time." But his extraordinary powers of concentration sometimes blind him to the normal flow of human events. Having approved staff vacations months in advance, he may be shocked to discover someone gone. "Who said they could take vacations?" he has been known to ask.

Aspin has no family life of his own -- he is, in Mencken's phrase, "unencumbered by issue or debt." He has a habit of calling staff meetings at night or on weekends. When one such gathering drifted into the dark hours of a November Wednesday, Gentilly finally nudged him: "Les, it's getting late. Some people have to get on the road."

"Why?" he asked blankly.

"It's Thanksgiving, Les. A national holiday. Remember the Pilgrims?" ASPIN HUNCHES down like a bespectacled turtle as he answers questions from two dozen union men in Janesville, Wis. They have risen early on a Saturday morning for coffee and conversation with their man in Washington. Everyone seems to know him as "Les." In a town where the big job is assembling Chevies and Cadillacs, questions about Japanese car quotas and the location of GM's new Saturn car plant take precedence over MX missiles.

One day earlier Aspin had met with General Motors chairman Roger Smith in Washington, but the chances of heavily unionized southern Wisconsin winning out over Sunbelt applicants for the Saturn plant seemed slim. Aspin dances around the question: "I hear ya, I hear ya." To other questions, his replies roll out in halting circumlocutions that include all sides of the argument and sometimes end with multiple- choice answers. "He gives you a definite 'maybe,' and tells you it's the final answer," laughs a carpenter.

But it works. Aspin is accessible, and his rumpled suits and charming manner win votes. No one seems to mind that his only Wisconsin residence is a summer house on Lake Beulah that remains closed during most of the year. On his frequent weekend trips to his district, he sleeps in motels like a traveling salesman. He has been elected eight successive times in a traditionally Republican district.

WITH THE Senate in Republican hands, Aspin is in a position to outflank Georgia's Sen. Sam Nunn, the ranking Democrat on the Senate Armed Services Committee, as his party's chief spokesman on defense. In a recent speech Aspin established the tone of his regime with a new working slogan: "Defense without nonsense." He attached the Reagan administration for a world view that calls the Soviet Union an "evil empire" while taking "almost a casual view of the threat of nuclear war." Liberal Democrats, he said are often guilty of the reverse: "The left fears nuclear war and is too casual about Soviet goals."

Aspin suggested Democrats take the middle ground: "A healthy respect for the dangers of nuclear war, and a healthy respect for the dangers posed by Soviet ambitions." He also exhorted Democrats to shed their "Dr. No" image on defense issues and establish themselves as the party that is "for" something, not only carving away at the Republican defense budget, but favoring the addition of certain military items neglected by the administration.

"You've got to cut the budget below where you really want to be," he said in the manner of a master bargainer at the Marrkesh bazaar, "then add on some things you favor that bring it back up to the figure you're willing to accept."

None of this endears Aspin to many professional military leaders who vividly remember his years of whiplashing them with press releases about sloppy spending. NATO Supreme Commander Alexander Haig was the subject of one release that noted he transported his dog, Duncan, around Europe at federal expense; Haig reimbursed the government. Aspin once rleased information on an antiship missile with a flawed guidance system; in a simulation test, it locked on to an island off the California coast rather than the ship it was supposed to hit.

His best-known release, however, went straight to teh heart of anation of dog-lovers, exposing chemicals warfare experiments that were gassing beagle puppies. He suggested complaints be sent to then Armed Services Committee chairman F. Edward Hebert of Louisiana. "He got gobs of mail," chuckles Aspin. "Whole bagfuls of mail!"

Aspin's ascension to the armed services chairmanship was received without enthusiasm by uniformed Pentagon brass. "They were appalled," sai a senior defense department official. "Before, it was three cheers for a strong defense. Now you have a smart, tough guy who you can't beat over the head witha pork barrel running your most supportive committee."

Even so, Aspin may be far friendlier to the military than his past would suggest. "Les is probably more pro-military than the average Democrat in the House," says his friend and mentor, former defense secretary Harold brown, "but probably less pro-military than the public at large."

Aspin's field is defense, but his passion is arms control, the high ground of strategic political science, a specialty that rests on the esoteric vocabulary of "throwweights," "warhead yield," "megatonnage," "fratricide" and "aggregate destructive capacity."

His arms control philosphy is simple and pragmatic. "What matters is what works," he says. "The whole goal of arms control is to take away any incentive for a first strike, not just the ability for a frist strike. If we can reduce the numbers of warheads or reduce defense budgets, that is frosting on the cake. But the real meat and potatoes of arms control is to tereduce the chance of nuclear war breaking out."

To Aspin, everything is context, linkage, workability. "I was in favor of the MX on a racetrack coupled with SALT II," he says, speaking of two abortive initiatives of the Carter administration. Today he favors limited deployment of the MX as a bargaining chip in arms control negotiations. "To some people, MX is MX is MX. My position has always been alittle bit more complicated -- the MX in and of itself is neither good nor bad. It depends upon what else is going on in defense and in arms control . . . the context that it is being considered in."

Outrage over the year's first MX vote has settled down, but it is not gone."There are 20 months left in this Congress," says Rep. Norman Mineta (D-Calif.) "none of us is a one-issue guy. Les' status will be decided on how he runs hte committee, not just on MX."

Memories of front-page photographs of Aspin huddling with a White House lobbyist during the MX vote have dimmed. O'Neill sent Aspin a glossyprint of thepictuyre with the inscription: "Dear Les, Next time, let it be Les and Tip."

But Rep. Wolpe says: This has clearly left a very bad taste among large parts of the Democratic caucus. Les can restore his influence if he now leads the effort in blocking any further MX funding."

Congressman Edgar of Pennsylvania cautions: "What Les has to watch out for is another coup. It happened once, it can happen again."