He is a tough-talking New Yorker in a presidential coterie of cool westerners, a point man for the Reagan revolution in an increasingly skeptical Congress and an avid ice hockey fan who plays hard at politics inside and outside the White House.

Kenneth M. Duberstein, assistant to President Reagan for legislative affairs and Reagan's chief lobbyist on Capitol Hill, shuns the limelight.

But he finds himself in the center of brewing Capitol Hill storms over Reagan policies on issues ranging from the budget to Central America. As the administration has struggled in recent months to regain control of the congressional agenda, Duberstein, 39, has emerged as a key player in the White House West Wing.

A stocky chain smoker, Duberstein has brought a more aggressive, down-to-earth approach to dealing with Congress than did his mentor and predecessor, Max L. Friedersdorf.

"While he's a good slap-on-the-back, sort of cocky, jolly Brooklyn character, Ken is also tough," a close associate in the White House said. "He's a smiley-tough guy. He definitely knows the seriousness of the game he's playing; he definitely knows when to say no."

"I think he's survived the baptism of fire," said Sen. Paul Laxalt (R-Nev.), considered the president's closest friend in Congress.

Even so, Duberstein is caught in strong political crosscurrents. Internally, the White House is torn by rival strategies for dealing with Congress. Externally, the administration is grappling with a shift of power away from Reagan on Capitol Hill.

In contrast to economic issues on which Reagan seemed to enjoy momentum and a mandate during his first two years as president, the agenda has shifted to the far more contentious questions of Central America, defense spending, the MX missile and nuclear arms control.

Reagan's senior advisers have been sharply split over strategy and tactics in recent weeks. The legislative strategy team under chief of staff James A. Baker III--which includes Duberstein, presidential assistant Richard G. Darman and budget director David A. Stockman--has urged Reagan to reach out to allies and foes on Capitol Hill, compromising when necessary.

But national security adviser William P. Clark and Defense Secretary Caspar W. Weinberger have advocated a hard-line strategy depending, instead, on Reagan's ability to change the minds of reluctant legislators.

While Duberstein has attempted discreetly to bridge these rival camps, helping Clark with Reagan's recent speech on Central America and the Senate confirmation of Kenneth L. Adelman to head the Arms Control and Disarmament Agency, the rivalry remains.

Meanwhile, on Capitol Hill, the Republican administration no longer commands the coalitions that won Reagan dramatic victories during his first two years in office. With the Democrats having gained 26 seats in the House in the 1982 elections and Senate Republicans growing jittery about 1984, the administration lacks an effective legislative strategy, according to one senior official.

"We really don't have a coherent strategy. That's what's happening right now in this whole budget-process breakdown and problem," the official said. "We don't have some strategy that says, 'we have no assets in the House, we can't move anything,' so how do we cope with that when we have all these things that have to get done in the next 18 months?

"Maybe we try and find some way of an administration-Senate axis that has enough standing and bipartisan aura about it that the House is induced to move, rather than be recalcitrant, partisan, irresponsible and political," the official said. "Well, we don't have that strategy."

"The strategy fell apart" on the budget, according to a Senate Republican leadership source. "It was a great idea, but it isn't there now."

When Duberstein took over from Friedersdorf after the budget and tax victories of 1981, such daunting problems were not yet evident.

As chief Reagan lobbyist in the House, Duberstein had been instrumental in putting together the coalition of Republicans and "Boll Weevil" Democrats that carried the economic program. But when Friedersdorf left the post for health reasons, White House officials had doubts whether Duberstein was ready for a job that also required him to build bridges to the Senate.

"I think that Max and Ken were both creatures of the House--what they knew as an institution best was the House. But the Senate is a different animal, with the courtesies, the gentleman's club," a White House official said. "It was better that Max went first. Max had broken into the club. Ken sort of inherited the membership."

The Senate leadership source said, "A lot of people questioned at first if he was up to the job. Max was an establishment person, and here comes Ken, he cut his teeth on the House side, on the '81 coalition. People over here don't think as highly of the House."

But this official said Duberstein's contacts on the other side of the Capitol "turned out to be one of his big pluses."

In the House, Duberstein earned a reputation as being "persuasive and persistent," Minority Whip Trent Lott (R-Miss.) said recently. "He can be tough when he needs to be. He can be blunt. The dimension he brings is that of a street awareness of a member's survival. He knows my district, what my base is and where my heart is."

"As an adversary, I respect him," said Rep. Thomas J. Downey (D-N.Y.), who will be leading the fight against the White House on the MX missile. "This is a very sophisticated and capable political operation."

One aspect of that operation is taking care of small things for members of Congress: presidential photographs, White House tour passes, positions at the table with Reagan. Sometimes, a slip-up can be troublesome.

Once, after Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) had to wait at the White House gate for 10 minutes because guards did not recognize him and he had no identification, Baker became angry in a meeting. Later, he presented an embarrassed but good-humored Duberstein with a big red tag: "U.S. Capitol, Authorized Visitor, S-230."

Politically, Duberstein has reached beyond Republicans and conservative Democrats who are Reagan's central allies. For example, he fought House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) on the Reagan tax cut but later struck up a friendship with him that is shared by the president.

The relationship was dubbed the "Reagan-Rostenkowski vote-gathering machine" by the congressman last year in a speech.

It has proved valuable to the White House at a time when rhetoric has sometimes grown heated between Reagan and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

Earlier this year, at a private White House dinner for Rostenkowski and several other members, Rostenkowski expressed his willingness to help Reagan on some key issues. When the administration asked Rostenkowski to tour the Caribbean, he invited Duberstein along. Rostenkowski came back a supporter of Reagan's Caribbean Basin Initiative.

Duberstein reportedly also used the trip to lay the groundwork for the Social Security rescue plan compromise that later passed Ways and Means. On the night the compromise was approved by the House, Rostenkowski invited Duberstein to a dinner at which no other Republican was present.

"It shows the advantage of Ken's personal style," a White House official said. "Rostenkowski is the classic example of a guy who really doesn't want to argue the merits of anything, who really doesn't want to read any piece of paper. What he wants to do is slap on the back, tell stories, play golf."

"He knows how to count votes," Duberstein said of Rostenkowski. "His personality is outward-going, and he's a solid pol."

In an atmosphere often permeated with ideological distrust, Duberstein has had the delicate task of reassuring GOP conservatives while reaching out to Democrats. He describes himself as a "believer in Reagan," but some conservatives were wary at first because he had been an aide of senator Jacob K. Javits (R-N.Y.).

Duberstein also was a congressional liaison for the General Services Administration and the Labor Department in the Nixon and Ford administrations.

"There was considerable skepticism and doubt among conservatives," Laxalt said. "In part, it was due to the old connections."

But, Laxalt added, "Most of the members now feel he's worked well. I don't hear of any discontent."

"They could use a few more Ken Dubersteins up here," Lott said.

Downey, who was on the Caribbean trip, said Duberstein "talks to both sides. Since I think this administration is wrong in just about everything it does, it's nice to have someone to talk to.

"He's a kid from Brooklyn, and I'm a kid from Queens, and we both have the same love for Chinese food, baseball and pizza," Downey said, making the point that Duberstein stands out from the California-Texas axis at the White House. "The world is as much corned beef and cabbage as it is golden raisins. The fact is, Ken gives you the other side."

Inside the White House, where Stockman provides the numbers and Darman the larger concepts, Duberstein brings "reality therapy" to legislative strategy sessions.

"It's identifying what will fly and won't fly on the Hill," Duberstein said. "Where the consensus is at the current time, how far you can move it along, what are the pitfalls, the obstacles--how does something work out although on the surface it may look very muddy."

This was his task when the Adelman nomination ran into stiff opposition in the Senate. Duberstein spent eight hours one Saturday grilling Adelman about every aspect of the controversy swirling around his nomination.

On Sunday, he sent H.P. Goldfield, a White House lawyer, to New York City to examine Adelman's files at the United Nations. Duberstein also asked Goldfield to bring back a hot pastrami sandwich on rye. Goldfield found the files in order but ate the sandwich on the plane coming home that night.

After the Adelman session, Duberstein reached Majority Leader Baker at home to tell him he was satisfied with the nominee.

"That's enough for me," Baker replied, according to a Senate Republican leadership source. "Baker put his reputation on the line at Duberstein's word."

Adelman was confirmed. But Duberstein has had his share of setbacks.

In the struggle with Congress over the fiscal 1984 budget resolution, Duberstein and the others working under chief of staff Baker were said to be convinced that Reagan could have won more money for defense and gotten greater cuts in domestic spending if he had compromised sooner--rather than trying to hold out, as Weinberger and Clark had urged.

"He was agonizing over it. Ken was in a position where he basically couldn't do anything," a Senate leadership source said.

"I don't think he was a player on that one," Laxalt commented.

A friend said the "low point" for Duberstein was the April 7 phone call Reagan made to Senate Budget Committee Chairman Pete V. Domenici (R-N.M.) while Duberstein and Darman were standing by in the Oval Office with Weinberger and Clark.

The friend said Duberstein "agonized" because he knew the defense spending levels Reagan was offering would anger the Republican-controlled Senate Budget Committee and be rejected. He was correct. After the call, the committee voted half of the defense spending increase originally sought by Reagan.

Recently, Duberstein argued with other White House officials about who should give the first speech at the politically potent ceremony to sign the Social Security rescue bill. Duberstein thought it would be a nice gesture if the White House let O'Neill talk first.

But others disagreed, and the next day Reagan stepped to the podium first.