On his days off, he is an accomplished weight lifter who once bench pressed 385 pounds. On the job, chief White House political aide Edward J. Rollins has emerged as an administration "enforcer" who says he believes in "protecting the president" and punishing disloyal Republicans.

In less than four months as successor to longtime Reagan aide Lyn Nofziger, Rollins, 39, has emerged as one of the most outspoken, hard-nosed and controversial spokesmen for his embattled president.

He also has won the secret admiration of some less outspoken Republicans who say that the White House has focused too much on bipartisan compromises with Democrats and too little on the partisan demands of what promises to be a difficult year for the GOP.

"Some Republican congressmen think they can do whatever they like because Ronald Reagan is a gentleman," one administration insider said. "They are taking blatant advantage of Reagan's good nature. It isn't helping the president, and he needs someone to do something about it. If Ronald Reagan surrounds himself with people of identical personality, he will be run into the ground."

The self-designated "someone" is Rollins, a Californian who was an aide to the Republican speaker of the state assembly when Reagan was governor.

Rollins, though not an ideologue, has become an overnight hero to some conservative Republicans for his questioning of the political loyalty of Sen. Bob Packwood (R-Ore.), a moderate whose repeated digs at Reagan have made him the least favorite Republican in the White House.

Talking to reporters in the White House Rose Garden yesterday, Reagan held out an olive branch to Packwood, who said last week that the president's willingness to accept deficit budgets has "removed the glue that held everyone together in the Republican Party."

Reagan said he wanted contributions made to the Republican senatorial campaign committee, which Packwood heads. But the White House, acting through Rollins, has refused permission for Packwood to distribute a fund-raising letter signed by Reagan.

Some think Rollins' role will be a brief one and that he ultimately will be sacrificed in the interest of party unity.

However, Reagan rarely has jettisoned any aide for displaying an excess of loyalty, and it is generally believed in Republican leadership circles that Rollins will survive politically.

His partisan qualities are likely to be more valued, it is believed, after the present budget impasse is ended and the normal combativeness of election-year politics takes over. And it is widely recognized, even among Rollins' critics within the administration, that someone has to play the tough guy.

One friend of Rollins said Rollins made the decision to speak out for Reagan, recognizing that others in the White House, notably chief of staff James A. Baker III, Rollins' boss, were not about to give the green light for an attack strategy.

"He didn't tell them," the friend said. "He has chosen the role for himself, sort of like Charles Bronson in 'Death Wish.' He didn't seek permission."

This has been Rollins' style since he took over from Nofziger in January and a week later plunged into controversy by telling the Washington correspondent for the California-based McClatchy Newspapers that the president's daughter, Maureen, a Senate hopeful, "has the highest negatives of any candidate I've seen."

For good measure that was followed by a candid description of Maureen Reagan's negatives: "Her campaign has not caught fire and she has serious financial problems. She's been strident on some issues, and, while the president has been scrupulously neutral, there's an impression that Maureen is not the overwhelming choice of the Reagan boys."

This assessment prompted Maureen Reagan to telephone her father, who summoned Rollins and instructed him to refrain from any further assessment of Republican primaries.

"It was not an auspicious start," Rollins acknowledged.

In February, Rollins plunged into another controversy when he was quoted as having told a Georgetown University class that the administration had pressured Sen. Roger W. Jepsen (R-Iowa) into voting for the airborne warning and control system (AWACS) aircraft for Saudi Arabia.

"We just beat his brains out," Rollins was quoted as saying.

After this controversy had quieted, Rollins became the point man in a White House effort to rebuke Packwood. And Rollins said last week that Republicans who criticized Reagan should be "disciplined," a remark that earned another Rose Garden rebuke from the president, who had been advised by Baker that the comment had not pleased GOP congressmen.

While Rollins' outspoken style has produced controversy, the technical and coordinating efforts of his political unit have won unpublicized approval among GOP professionals at the Republican National Committee and in Congress.

Working out of a first-floor office in the Executive Office Building, Rollins and his deputies have drawn up a carefully coordinated plan for providing assistance to marginal Republican incumbents and promising Republican congressional candidates.

His staff is small--11 compared with the 38 Nofizger mustered early in the administration--and seven of these are support personnel. One deputy, Lee Atwater, a veteran southern campaign manager, is rated highly among Republican professionals.

Despite a widespread assumption in political circles that Reagan will not seek a second term in 1984, Rollins operates on the assumption that he will. This means, he says, that the White House must pay careful attention to maintaining the GOP gubernatorial base in Reagan's home state of California, where there is an open race, and in Illinois and Pennsylvania, where GOP incumbents are seeking reelection.

It also means establishing a system of priorities for the districts in which the president's personal involvement could make the difference between victory and defeat. These priorities are being determined largely by the polls of Richard B. Wirthlin, whose former partner, Richard Beal, is in charge of "future planning" and meets often with Rollins.

To the political office has been left such thankless tasks as telling the 130 presumably safe GOP congressmen that they cannot have Vice President Bush in for a fund-raiser, or informing Republican members of Congress who face token primary opposition that they can not get a letter of support from Reagan because he refuses to become involved in primaries.

Lack of involvement in electoral politics is a hallmark of the Reagan style. Those long associated with him see him more as a communicator than an electoral politician.

One Republican familiar with the Nixon and Ford White House political operations made the point that both of those presidents were more involved in day-to-day political activities than is Reagan or most of the top members of his staff.

The other side of the coin, however, is that midterm elections under both these Republican presidents were competitive affairs among the various GOP campaign committees.

The current White House political unit is trying to replace this with a coordinated campaign effort that can direct surrogates, political resources and money to key congressional districts.

In this effort, Rollins' overriding objectives are to protect the president and send him and his surrogates to the districts where it will do the most good for Republican candidates.

"We're thinking ahead," he said. "Everything we do in '82 helps us get ready for '84."