At 7:30 in the morning, the Rayburn House Office Building is a vast marble maze of quiet. But in one ground-floor corner office, an enormous voice is already shaking the silence like a foghorn in a phone booth.

The baritone bellow belongs to Dan Rostenkowski, 11-term Chicago Democrat and the newly appointed chairman of the Ways and Means Committee, blatting out the strategy for the tax bill which tomorrow will be reported out of committee and offered to the House to compete with the three-year, 25-percent, across-the-board cuts proposed by President Reagan.

"It's awesome," says Rostenkowski of next week's floor battle in the House. "I mean, you're talking about the president of the United States. But we've been sparring and sparring and now the audience is starting to say, 'You'd better start hitting each other. We came here to watch a fight.'"

And when the final votes are tallied, the winner may determine more than tax policy. House Democrats, stunned by the early legislative onslaught from the White House, are perceived as lacking dynamic leadership. But "if a Democratic committee chairman can defeat Ronald Reagan, a man who is larger than life," says one veteran member of Ways and Means, "then Rostenkowski is going to look very, very strong for the leadership. It adds an emotional surcharge to the proceedings."

At 6 feet 2 and 225 pounds -- with the big-beef of a Midwest ward heeler, the constantly waving massive arms of pro baseball player he almost became, and a girth bespeaking decades of potato dumplings on the campaign circuit -- it's hard to imagine Rostenkowski losing a fight. He's a man who nursed an eight-year grudge against Abraham Ribicoff before crushing one of the senator's pet projects in a committee showdown; he suffered humiliation at the hands of the McGovern liberals in 1972 and endured to see them discredited; and he outlived the animosity of Carl Albert to become a major contender among House heavyweights. He's a man who will give a lot to win, and even hard-line Republicans give the 53-year-old product of the Richard Daley machine at least a fifty-fifty chance.

But in the tax fight, what he gains in votes he could lose in respect. Democratic critics say that in forming a consensus for his bill (which skews tax cuts to the $15,000-to-$50,000 salary range and makes the third-year-cuts conditional upon economic improvement) he conceded too much to the White House. Republicans say that even if he wins he loses, because over months of negotiations his bill has become similar to Reagan's. "If you say my bill looks like Reaganhs, baloney!" Rostenkowski shouts at ear-numbing volume. "I think that his looks a little bit more like mine." Coming of Age in Congress

For most of Dan Rostenkowski's two decades in Congress, that kind of language would have been unthinkable. Until a few years ago, he was widely regarded as a lackluster protege of the Daley organization, a get-along-go-along legislator whose sporadic notoriety derived from engineering compromises (like the weakened version of President Carter's hospital cost-containment program) or advocating congressional pay increases. No Solon, perhaps ("I plead guilty to the fact that I'm not a technician"), but praised by his staff as a hard taskmaster with a warm concern for his aides, and by his colleagues as a gregarious communicator, expert head-counter, seasoned enforcer and dependable arbiter of closed-door consensus.

"The chemistry of Rostenkowski is he's political," says Rostenkowski, who routinely speaks of himself in the third person. "I'm the physical, as opposed to the student."

He might have continued indifferently and indefinitely representing the predominantly Polish blue-collar workers of the Near Northwest Side who have given him over 80 percent of the vote in recent elections. But in 1976, two events converged to change his reputation.

The first was a bitter fight in a House-Senate tax-bill conference. Rostenkowski, who has served on the Ways and Means Committee since 1964, was tapped to fight a provision favorable to insurance companies introduced by then-senator Abe Ribicoff (D-Conn.). The role had relish: Back in 1968, Ribicoff had enraged Chicago pols by complaining of "gestapo" tactics at the Democratic Convention in Chicago -- which Rostenkowski had gaveled to order after Carl Albert lost control of the unruly throng and Lyndon Johnson ordered Rostenkowski to take over (thus making a long-term enemy of then-majority leader Albert). Eight years had passed since then. But Rostenkowski "has the best memory in Washington," according to one of his aides.

Rostenkowski recalls: "In the conference, Al Ullman [Rostenkowski's predecessor as Ways and Means chairman] called me in and said, 'Dan, somebody's going to have to be the tough guy here.' I said, 'Al, if you want me to be the tough guy, I'll be the tough guy.'" He was up against the heavyweights of the Senate side, including Russell Long (D-La.) and Lloyd Bentsen (D-Tex.), and nobody expected much from him. But, "I showed that if I studied I could participate. I must admit that I worked like a beaver." He "steeped himself for hour after hour in tax law," recalls a House aide who watched the "shoot-out," and "came back and stunned that entire audience" with his attack on Ribicoff's plan. It lost resoundingly.

"I went in the room and just kicked the brains out of them," a grinning Rostenkowski says now, smacking his heavy left fist into an open right palm. "Russell Long looked at me and said, 'Oh my god,' and all of a sudden I was getting all the telephone calls. I'd call Ullman and ask, 'Al, what do I do with this one? What do I do with that one?'"

The other event of 1976 was the death of Richard Daley, which freed Rostenkowski to be his own man and eventually to become, as the Chicago Tribune said last December, "very likely the most powerful Democratic politician in Illinois." The Second City

"His world in Chicago is more real than his world in Washington," says a longtime aide, and he spends as much time there as possible, leading some observers to believe that he intends to run for major some day. In Washington he keeps "a place in Southwest where he hangs his suits" and avoids the pomp and "folderol of long dinners," according to James Healey Jr., who has been on Rostenkowski's staff for 11 years, preferring to dine at "a fried chicken place out in Prince George's County." "I don't think he would know where any of the embassies are," says another aide.

Since coming to Congress in 1959, Rostenkowski has spent only nine weekends in Washington, and has not varied the pattern even after assuming the chairmanship: "I just fly up and back a few more times." When he was scheduled to appear on "Meet the Press" last weekend, he flew into Washington early Sunday and flew back immediately to rejoin his wife LaVerne and four daughters, aged 20 to 28, all of whom live in or near his district. "And then I came back here Monday morning," he says. "You can get pretty tired."

Even with the rasp of exhaustion in his voice, it is hard to believe that Dan Rostenkowski is tired. Sitting in his comfortable Rayburn office between the statue of the first black to play Othello and the color portrait of Richard Daley, the man in rumpled shirt sleeves radiates a raw animal stamina -- straining with syntax and gesturing wildly when the words won't come, pointing an emphatic finger ("he uses his bulk, in a sense, as a language," says an aide), looking listeners hard in the eye with the thick-lidded squint of a pol who knows not only where the bodies are buried but where the shovel is, speaking with a back-room candor that is both vulgar and refreshing. "Direct to a fault," says Healey.

He is the grandson of a Polish immigrant who built both the four-story brick house that Rostenkowski now lives in and the political tradition he inherited. "My grandfather ran for county commissioner with William Jennings Bryan and suffered the same defeat. My father became a state representative and then a councilman with Mayor Anton Cermak and stayed in the council for about 28 years." Rostenkowski attended his parish grammar school and then St. John's Military Academy in Delafield, Wis. From 1942 to the time he joined the Army, he accumulated 14 letters in four sports, but liked baseball best. After the war, it paid off. In 1949, the springafter he had started night school at Loyola, Connie Mack of the old Philadelphia Athletics asked him to try out at the Sarasota, Fla., farm club. But, "My mother was sick, and my dad called me and said, 'Come on home. You're never going to be a Lou Gehrig or a Babe Ruth. C'mon home, go to school. And I said, 'Yeah, Dad.' And he said 'Furthermore, you're a late swinger.' Now, in an introduction, everbody will always say, 'You know, Dan Rostenkowdki was always a late swinger.'"

Politics "just started to be a part of my life," he says. He joined the Democratic organization and shortly after his marriage in 1952, "I served in the state legislature in the same district that my uncle as a Republican and my father as a Democrat served: two years in the House and four years in the Senate." The Daley Legacy

He learned a political tradition in which "you just waited, built up credits" and watched "other people, extremely ambitious, burn out their fuses." By the late '50s, he felt he was ready to run for Congress, but Daley "wanted me to stay in Chicago for reasons that he as a politician thought were to his advantage: I was young, 28 years old, nice big long name -- Rostenkowski, no question about where he comes from, what he is, loyal. He said, 'You'll drink that Potomac water and we'll never see you again.'"

In those days, the Chicago machine looked on Washington "as a place for retirement. But I said, 'What we've got to do is send young people to Washington and have them just sit there and wait to become chairmen. Mr. Mayor, the South has won the war ever since Reconstruction because when all their people come to Congress, they stay there a long time.'" Daley was convinced, and Rostenkowski went to Washington at age 31, and started learning from the Dixiecrats. "They're uncomplicated and they're men of their word. They believe in trading. Organized Democrats in a big-city political organization are no different from southerners. Southerners are patient."

Patient: Rostenkowski has endured setbacks in the House (after becoming chairman of the Democratic caucus in the '60s, he was considered a comer, but lost in 1970 to Olin (Tiger) Teague of Texas in a bitter upset) and in his own party, during the convulsions of the 1972 convention in Miami when the liberal guidelines for delegation selection outraged many of the old-line party faithful. "They challenged us, and even though I was elected by 98,000 votes by the people, I was not seated." The Illinois delegration "had a young Spanish-speaking girl, we had two blacks, we took the president of a university. We just looked at what Larry O'Brien and Joe Califano and all those flaming liberals wanted when they put these rules together, and just put it in." Rostenkowski decided not to get mad. "You view this and then you start thinking, 'Why not just lay back, because this is going to pass.' And it is passing."

And Rostenkowski has endured, living his bicameral life, coming home to a wife who "gave up trying to analyze what congressmen do when we put a ceiling on our outside earnings." His family is very close, and he wears a gold medallion around his neck "with all their birth dates and our marriage date on it. Is this a cloverleaf or a shamrock? Maybe it's a shamrock. For a Polish politician!"

That heritage is an asset in Chicago, where Rostenkowski has his alternative future. "There's a great deal of speculation as to whether Democrats will control the House next time. If we don't, and I'm the minority ranking member, there's a lot of speculation that this will not satisfy my appetite and I would move over and try to become the mayor. Well, I think that every citizen of the city should want to be mayor and every congressman should want to be speaker.

"I don't know what I'm going to do. My wife would like to see me come home. Not to be the mayor of Chicago, though. But just to come home." c Assets and Deficits

It seems unlikely. Many House Democrats assume that Rostenkowski's present momentum will carry him eventually toward the positions of majority leader and perhaps even speaker. But he is quick to express confidence in the House leadership. "Everybody wants their taxes reduced," he says, but when the public finds out that services, too, will be reduced, House Speaker Thomas P. O'Neill "will be proven right. Tip O'Neill, in my opinion, is playing the long game."

So is Rostenkowski. With a safe seat (last year, his Republican opponent was a 75-year-old man who had never held public office, had no campaign committee and kept an unlisted telephone number), $274,580 in campaign contributions in 1980 (over $100,000 from business political action committees, according to a new study by Common Cause), a long memory and lot of punitive clout ("Everybody, at one time or another, will have some bill before the Ways and Means Committee"), he is gambling on the popular appeal of his bill and his brand of convivial pragmatism to convince potential skeptics and establish his future reputation with patience and credits.

He lost a little credit in forming the tax bill, changing his mind several times before arriving at the final version of the bill, first favoring a one-year tax cut, then two years with across-the-board cuts. "When I proposed this to my Democratic caucus, they almost threw me out," he says. O'Neill "just said, 'Goddam it, that's insanity ! That's the one thing that we've got.' And by God, he was absolutely right. . . I had really departed from basic Democratic principles."