Meet Robert H. Bork, mainstream jurist, a fitting successor to Justice Lewis F. Powell Jr. and a man whose confirmation would not alter the balance of the Supreme Court.

Meet Robert H. Bork, ideologue, extreme conservative and a man whose presence on the high court would jeopardize a broad array of constitutional rights.

In the five weeks since President Reagan nominated Bork, a judge on the federal appeals court here, two contradictory portraits of the 60-year-old jurist have been put before the Senate and the American public.

The Reagan administration would prefer to fight the confirmation battle on the more comfortable turf of Bork's qualifications and his philosophy of judicial restraint -- an argument that is "attractive to the mainstream member," said one senior administration official involved in the nomination strategy.

But Democratic senators and liberal opponents of Bork's nomination have forcefully and repeatedly denounced him, saying his scholarly writings and judicial opinions indicate that he would tip the court's balance on such matters as abortion, affirmative action and school prayer.

Perceptions of Bork are important. Polls indicate that those who view him as a moderate or conservative are likely to support him while those who see him as very conservative are apt to oppose him.

The White House has responded by portraying Bork as a man whose judicial philosophy is well within the modern constitutional mainstream.

In a July 29 speech on Bork's nomination, Reagan noted that Bork and Powell had agreed in nine of 10 cases reviewed by the Supreme Court in which Bork participated on the U.S. Court of Appeals for the District of Columbia Circuit. "It's hard for a fair-minded person to escape the conclusion that, if you want someone with Justice Powell's detachment and statesmanship, you can't do better than Judge Bork," Reagan said.

Last week, the White House distributed to some members of Congress and others a briefing book that stresses this view of Bork as a moderate to a much greater degree than White House aides say is planned for the president's speeches. The book takes on Bork opponents by rebutting specific criticisms of him and is part of a multipronged strategy that includes articles submitted to newspaper opinion pages and Bork visits to senators.

"Judge Bork's appointment would not change the balance of the Supreme Court," the book says. "In every instance, Judge Bork's decisions are based on his reading of the statutes, constitutional provisions and case law before him. A justice who brings that approach to the Supreme Court will not alter the present balance in any way."

Bork's legal philosophy, it says, "follows directly in the mainstream tradition exemplified by jurists such as {Felix} Frankfurter, {John} Harlan, and {Hugo L.} Black rather than the 'activist' trend which resulted in the invalidation of major New Deal legislation in the 1930s."

The book contrasts Bork's views, particularly on free speech, with those of his "more conservative colleague" on the circuit court, Antonin Scalia, who became a member of the Supreme Court last year.

The book opens with a roster of Bork's actions that have most angered conservatives, including his criticism of a balanced-budget amendment and of measures that would have stripped federal courts of jurisdiction over such issues as busing, abortion and school prayer, and emphasizes Bork rulings in favor of blacks, women, homosexuals and unions.

For example, the briefing book notes that Bork opposed the idea of a balanced-budget amendment to the Constitution, quoting from a 1979 article Bork wrote for The Wall Street Journal. The White House noted that Bork had said such an amendment could create "nightmare litigation" that would threaten "judicial dominance in the budget process."

Reagan has campaigned for a balanced-budget amendment to the Constitution. The briefing book omitted some of Bork's favorable comments about such an amendment in the same article. Bork said the "case for it is compelling" but then raised questions about whether it would work.

Bork's criticisms of a raft of Supreme Court decisions were made while he was in academic life and do not mean that he would vote to overrule them on the bench, the briefing book emphasizes.

White House officials acknowledged the book is partly a defensive move, triggered by opponents' attacks on Bork.

"Bork is going to be interrogated on every aspect" of his opinions, said one senior official. By putting the book out, "you've tempered a little of the argument by saying, 'On this issue, here he is.' "

This official said "some portions" of the document "represent a response to charges that have already been made."

The book was a joint effort involving the office of White House counsel Arthur B. Culvahouse Jr., the Justice Department and outsiders close to Bork, including some who worked under him as solicitor general. The briefing book also includes a 2 1/2-page defense of Bork's role in the "Saturday Night Massacre," when, as solicitor general, he fired Watergate prosecutor Archibald Cox after Attorney General Elliot L. Richardson and Deputy Attorney General William D. Ruckelshaus refused to fire Cox and resigned.

Bork opponents characterized the White House briefing book as a "campaign of disinformation," in the words of Ralph G. Neas, executive director of the Leadership Conference on Civil Rights, a consortium of groups lobbying against the nomination.

"They're attempting to repackage Judge Bork but they can't change the contents," Neas said.

To the extent the administration is forced to debate specifics of Bork's record, he said, "The White House strategy plays into our strategy."

"It's part of an orchestrated effort, being played out very much in the last week or so to make Bork over in the cloth of Justice Powell, to say he's centrist, to say he's flexible," said Melanne Verveer of People for the American Way, a liberal group that is in the forefront of the anti-Bork campaign.

"Obviously, their rhetoric is a lot more toned down than what we would have expected and what we heard the first 24 hours after the nomination was made," she said.

One senior White House official said the administration's "strategy didn't change" as a result of the opposition. However, he said, "Simply put, when you have a man who has written and said as much as he has, we felt that we ought to fairly present the record in terms of what he has said.

"The document is in our mind a very scrubbed one -- {we} tried to make it fair," the official said.

Another report last week, by the Public Citizen Litigation Group, a consumer-oriented public interest group founded by Ralph Nader, presented an entirely different Bork: not only a conservative, but a judge willing to cast aside adherence to judicial restraint in order to achieve desired results.

In cases in which the appeals court judges disagree, the report said, "One can predict his vote with almost complete accuracy simply by identifying the parties in the case."

For example, the report said, in seven non-unanimous cases in which public interest groups sued to overturn a regulation, Bork voted in favor of the agency each time. But in eight split cases in which businesses challenged agency action, Bork voted each time to overturn the agency.

"When a private corporation or business group . . . sued the government, he was a judicial activist," the report said.

Administration officials criticized the report as an inaccurate portrayal becaused it focused on cases that were not unanimous.

Conservative activists, who in their direct mailings and other statements stress that Bork's nomination offers the chance to reshape the Supreme Court, assert that the difference between their portrayal of Bork and the administration's is a matter of emphasis.

"Some of us emphasize the judicial philosophy and the possible ramifications of it more than, say, the White House. Comparing him in 90 percent of the cases to Powell, well, it's the other 10 percent that's a step in our direction," said Daniel Casey of the American Conservative Union.

"We're not talking about a different Bork," Casey said, referring to the White House effort. Reagan, he said, "is talking about the most qualified nominee in the country and answering the charges that he's a radical. I'm saying . . . by the way, also he's going to begin turning the court back."

But other conservatives have expressed outrage at the portrayal.

Philip B. Kurland, a conservative professor at the University of Chicago Law School, termed efforts "to repaint Robert Bork as a closet liberal" an "assault on Bork's integrity."

"To make Bork over in the image of a Lewis Powell, a Robert Jackson or a Felix Frankfurter, as they would seek to do . . . " Kurland wrote in a letter to various law publications, "is to give the lie to Bork's public extrajudicial professions of his beliefs."