President Reagan's tax-overhaul proposal spells relief for many taxpayers and headaches for others who would lose cherished preferences and deductions. But for Chairman Dan Rostenkowski (D-Ill.) of the House Ways and Means Committee, the Reagan plan spells Opportunity with a capital O, starting tonight when the 57-year-old Chicagoan makes his prime-time national television debut giving the Democratic response to Reagan's tax address to the nation.

The gruff and burly Rostenkowski, who shares the penchant for malapropisms of his political patron, the late Chicago mayor Richard J. Daley, is not a threat to Reagan's title as "Great Communicator." But when the issue moves off television and into the halls of Congress, Rostenkowski will be in his element.

"What you have to understand about Danny," said a Republican who has watched him closely for the past 20 years, "is that he doesn't care much about the tax code, and he sure as hell is no reformer. What he cares about is control and power. He's in control on this issue, and he's going to use it to gain power."

Interviews with many of Rostenkowski's colleagues last week found almost universal agreement that the chairman will use the battle over tax simplification to settle some old scores with the Reagan administration and to improve his longshot chances of becoming the next speaker of the House.

"This is his last shot," said a Democratic member of Ways and Means, reflecting the widespread speculation that Rostenkowski will leave the House by 1988 if he is not speaker, "and he intends to give it all he's got. Besides," he added, "he's ticked off at the way Reagan's people have handled him."

"Sure, I'm irritated," Rostenkowski said in an interview. "They the Treasury officials handling the tax bill haven't talked to me for 2 1/2 weeks. All I know about their proposal is what I read in the papers. I'll be interested to see how they defend some of the things they've supposedly done."

Watching the Treasury negotiations with various Republican legislators and key interest groups, Rostenkowski expressed a hard-nosed Chicago pol's skepticism about the professionalism of the administration's brokers.

"They made their deals," he said. "I just hope they got something in return. They better understand that their package will be the high-water mark for reform . We aren't going to be able to regain any ground they gave away."

Switching metaphors again, Rostenkowski added, "I'm not going to give them a chance to jump off the train by denouncing them. I'm a Democrat interested in a fair tax system. If a Republican president wants to come into the pool with me, I'm not going to keep him out."

Such comments are regarded by the chairman's Ways and Means colleagues as part of his positioning or the real fights that lie ahead. Administration officials put down Rostenkowski's pique as irritation that he was cut out of the bargaining process of the past few weeks, and so was denied the opportunity to make some of the deals himself. They discount him as a threat to their plans.

This is not the first time that Rostenkowski has gone head-to-head with Reagan or with Treasury Secretary (and former White House chief of staff) James A. Baker III. Reagan and Baker beat him publicly in 1981, his first year as chairman, when they passed the three-year, across-the-board tax cut.

They lured Rostenkowski into making substantial concessions, then went behind his back and put together a Republican-southern Democratic coalition that defeated his compromise bill on the House floor. The next year, 1982, they bypassed Rostenkowski and got their follow-up tax bill enacted through Senate leadership.

Both Republicans and Democrats in the House believe that Rostenkowski is aching to get even -- and has done everything possible to assure himself of the leverage to gain his ends.

He got Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) to stack the committee with 23 Democrats and only 13 Republicans -- a larger Democratic advantage than overall House numbers justify. He has reconfirmed the personal loyalty of every new Democrat named to the committee since he became chairman.

Rostenkowski's attention to detail is characteristic of the Chicago Democratic tradition, where virtually the first commandment is "protect your base." Rostenkowski operates by that maxim. While still in his twenties, he inherited the job as 32nd Ward committeeman from his father. He has kept it during the 34 years he has served in the Illinois Legislature and Congress.

Rostenkowski denies any wish to show up Reagan by transforming his tax-simplification proposal into a measure that the president might find politically unacceptable.

"I've served with seven presidents," he said, waving at the signed pictures on his wall from every chief executive since Dwight D. Eisenhower, "and every one of them has said he wanted to clean up the tax system. If you want reform, you've got to have the president in the trenches with you."

Rostenkowski said he is almost resigned to Reagan's getting most of the political credit for any tax simplification that passes. "Sometimes," he said, "I think I'm Colonel Bogey in "The Bridge on the River Kwai" , building the bridge for my enemy. But if we don't get reform, it's going to hurt my constituents. We've got to think what it means for them, and not for us as politicians."

Despite his disclaimers, some Republicans say Rostenkowski has set the stage for dominating the House-Senate conference, where the final version of the tax bill will eventually be shaped for Reagan's signature -- or veto.

He has established a precedent of taking only four House Democrats and three Republicans with him to conference, cutting out of the decisive action two senior Democrats -- Reps. James R. Jones of Oklahoma and Andrew Jacobs Jr. of Indiana -- who might resist his leadership. Among Democrats on his committee, it is believed that Rostenkowski has at least an implicit agreement with the four subcommittee chairmen who join him regularly as conferees -- Reps. Sam M. Gibbons of Florida, J.J. (Jake) Pickle of Texas, Charles B. Rangel of New York and Fortney H. (Pete) Stark Jr. of California -- that they will support his stand in conference, and he will protect their bills in the full Ways and Means Committee.

Some leading House Republicans have warned the White House that Rostenkowski may outmaneuver Sen. Bob Packwood (R-Ore.), the new chairman of the Senate Finance Committee, and exploit the ill-concealed differences among the Senate Republicans who will sit across from him in the conference. Rostenkowski could be responsible for sending Reagan an unpalatable bill, they warn, forcing the president either to swallow his principles or to be seen as the barrier to reform.

When this theory was put to Rostenkowski, he professed great admiration for Packwood as a "tough" negotiator, then smiled and said, "If I wind up winning in conference -- or, let me say, if the House wins -- the country won't be the loser."

Along the way to that conference, many colleagues speculate, Rostenkowski will also try to outmaneuver House Majority Leader James C. Wright Jr. (D-Tex.), who has claimed enough pledged votes to succeed O'Neill as speaker when O'Neill steps down next year.

"Danny isn't really trusted by the younger, reform-minded people in the House," said a longtime leadership aide. "They see him as an old-style, machine politician, which he is. But he's hugged this tax-reform issue so tight he sounds like Ralph Nader talking about it."

Behind this new posture, a veteran House Republican speculates, is the chance Rostenkowski sees to mousetrap Wright into the role of defending special tax privileges for the oil and gas industry -- whose leaders are political and geographical allies of the Texas majority leader. "Danny would love to nail Jim Wright and Ronald Reagan as the oil industry's protectors," a Ways and Means Committee Democrat said. "He thinks that would win him votes in the Democratic caucus for speaker."

Predictably, Rostenkowski denies any such strategem, but he has never disguised his ambition to be speaker. He thought he was on the ladder to that job, but lost out to O'Neill for the No. 3 post as majority whip in complicated maneuvering that surrounded the elevation of Carl Albert of Oklahoma to the speaker's job in 1970. Then Wright moved in behind O'Neill in the line of succession.

Colleagues say that Rostenkowski has made it plain to them in conversation that he does not want to stay in the House if Wright becomes speaker. Democratic politicians in Chicago say he could run for mayor in 1987 if Wright succeeds O'Neill.

Rostenkowski discounts -- but does not rule out -- the mayor's race. But he virtually confirms his up-or-out attitude toward the House. "I came here in 1958," he said, "and I've been here a long time. I'm a Chicagoan. The kids are gone. His wife LaVerne is home alone. It's maybe time for me to do something else, while I'm still young enough to do it.

"I came here when I was 29," he recalled. "I convinced Mayor Daley we ought to send young people to Congress so we could have a crack at the committee chairmanships that always seemed to belong to the South. He could see that, in that way, we could have a voice in national policy.

"I've been here almost 30 years now," he said, "and it looks like I'm going to have that voice."