Liberal groups are issuing critical reports describing the nominee as being far outside the mainstream of modern legal thought. Conservatives are fighting back with mailings describing him as a well-respected legal scholar. The Justice Department is bracing for a major struggle, holding "moot court" sessions simulating Senate Judiciary Committee hearings.

This is the battle that promises to be the 1988 sequel to the failed Supreme Court nomination of Judge Robert H. Bork: the nomination of University of San Diego law professor Bernard H. Siegan to the 9th U.S. Circuit Court of Appeals in California.

Before the Supreme Court vacancy created last year by the retirement of Justice Lewis F. Powell Jr., Siegan's nomination -- pending since February -- was expected to be the big showdown of 1987.

Many of the civil rights and other groups that teamed up to defeat Bork are targeting Siegan, whose hearings are to resume before the committee early next month.

"He really is far stranger than Robert Bork," said Art Kropp, president of People for the American Way, which released a report on Siegan last Wednesday. "Looking at the issues that we apparently reached a consensus on in terms of Bork, there are certainly grounds to defeat the nomination."

Liberals "have got to have a target, and it's Bernie's turn," countered Patrick McGuigan, legal affairs analyst of Coalitions for America, a conservative lobbying group. "It shouldn't be at all surprising that their next target is Bernie Siegan when you look at what they did to Bork."

In some ways, the Siegan hearings promise to be a reprise of the Bork debate, centering on ideology rather than character. Like Bork, Siegan believes judges should decide constitutional cases according to the framers' "original intent" and he has criticized the high court for decisions on constitutional issues including school desegregation, abortion and free speech.

The fight over Siegan will test whether the closely divided Senate panel has the stomach for further bitterness and whether it will apply the same standards to lower-court nominees as it did to Bork.

The Bork hearings, a committee aide said, made clear that the Senate will consider legal philosophy in assessing judicial candidates. "It will never rise to the level that a Supreme Court nominee does, but you've got to look at these people carefully even when they're nominated for lower courts," the aide said.

Rejection of Bork does not "necessarily augur anything" for Siegan, Justice Department spokesman Patrick S. Korten said. "Bernie is first of all being nominated for the circuit court of appeals. If the Senate can confirm Robert Bork unanimously for the court of appeals, I see no reason why they can't confirm Siegan . . . . There is simply no justifiable reason to deny him confirmation unless you're some kind of liberal ideologue who can't tolerate having people on the court who are of a conservative bent."

Siegan's opponents contend that appeals court nominees deserve the same scrutiny as potential Supreme Court justices, since appeals courts are, as Nan Aron of the Alliance for Justice said, "the courts of last resort for the majority of cases."

Kropp said, "One of the things that has ended up being an embarrassment for the committee is the lack of attention that has been paid to some appeals court nominees. It came back to haunt them" on Judge Douglas H. Ginsburg.

Before Ginsburg withdrew from consideration for the high court, questions were raised about conflict of interest, based on his statements to the committee when nominated to the U.S. Circuit Court of Appeals for the District of Columbia.

Siegan, 63, who became friendly with Attorney General Edwin Meese III when Meese taught law at San Diego, takes original intent further than Bork in some areas.

He concludes, for example, that Brown v. Board of Education, the 1954 desegregation ruling that "separate but equal" public schools violate the 14th Amendment's guarantee of equal protection, "is not based on original understanding."

Instead, Siegan argued last year in his book, "The Supreme Court's Constitution," that the court should have found that segregated schools violated black children's constitutional right to travel.

"Original understanding provides little authority for the construction that the court has accorded in the school segregation cases," he wrote. "Although such segregation is totally repugnant in modern society, it does not follow that the Constitution necessarily provides relief in this area."

Siegan also has said he believes that the First Amendment's establishment clause, which provides that "Congress shall make no law respecting an establishment of religion," does not apply to the states, as the Supreme Court has held since 1950.

"By placing a limitation on the authority of the central government to advance a national religion, the establishment clause, as originally drafted, safeguards the powers of the states to sponsor or further religions of their own choosing," he wrote, referring to the " 'wall of separation' that supposedly exists between church and state."

While Bork contends that courts should be deferential to the will of majorities as expressed through legislatures, Siegan takes the libertarian view that courts should be willing to strike down an array of welfare and regulatory statutes -- such as minimum-wage legislation, environmental laws and zoning regulations -- that interfere with the economic liberties that he believes were intended to be the centerpiece of constitutional protection.

Siegan defends the Supreme Court's use of "substantive due process" to invalidate welfare and New Deal legislation, including the court's repudiated 1905 decision in Lochner v. New York overturning a state law limiting bakery workers' hours as a violation of the freedom of the employers' and employees' freedom of contract.

"The evidence is very persuasive that Lochner was a legitimate interpretation of original meaning," Siegan wrote.

In a 1985 lecture in honor of Siegan's late wife, Bork criticized Siegan's approach, saying that, while it "has many attractions" as a matter of economic philosophy, it "works a massive shift away from democracy and toward judicial rule."

In a letter to Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.), Harvard Law School Prof. Laurence H. Tribe said, "By essentially endorsing the use of the Constitution to invalidate such social-welfare measures as minimum-wage legislation, Mr. Siegan reveals himself to be not a judicial conservative but an ideologue of the right."

Tribe termed Siegan's interpretation of Brown "so bizarre and strained, so incompatible with meaningful enforcement of the right to integrated education and so at odds with ordinary ways of thinking about constitutional law as to bring into question both Mr. Siegan's competence as a constitutional lawyer and his sincerity as a scholar."

Siegan does not dispute that many of his views are at odds with modern constitutional jurisprudence.

"I have strong disagreements with the U.S. Supreme Court. I also have strong agreements with the U.S. Supreme Court," he said in a telephone interview from La Jolla, Calif., where he lives in mystery writer Raymond Chandler's old house. "One writes a book about the excesses of the court. I didn't talk about all that I agree with."

However, he argued that he would be willing and able to put aside those views and follow the high court's dictates on the 9th Circuit, which covers nine western states.

"I'm an honorable person," he said. "The obligation of a circuit court judge is to follow what the Supreme Court says. I hope to do that as best I can. I have lots of views . . . . I don't think any of those views are strong enough for me to dishonor my oath of office."

In his first committee appearance, Siegan promised to follow Supreme Court precedent. "My thinking is totally irrelevant," Siegan said of his libertarian philosophy. "The purpose here as an appeals court judge is to carry out the will of the Supreme Court and certainly not Bernie Siegan's will."

For example, Siegan said, he would abide by the court's view that the establishment clause does apply to the states. "As a judge, I would not dream of quarreling," he said. "I would be laughed off the block if I were to say otherwise."

Siegan's supporters said this promise should essentially end the inquiry. "There just cannot be a person in the world who agrees with every aspect of prevailing case law, which means everbody who goes on the bench," Assistant Attorney General John R. Bolton said.

Liberal Harvard Law School Prof. Alan M. Dershowitz also backs Siegan, writing that, although his views are "indeed iconoclastic," no "single orthodox view of Constitutional adjudication should be deemed the established or mainstream one, so long as the nominee has a commitment to protecting liberty and individual rights. I am confident that Prof. Siegan fits comfortably within this criterion."

Opponents say Siegan's views are so far out of line as to merit rejection.

"He is bound to {follow precedent}, but the question is whether the Senate Judiciary Committee ought to confirm someone whose views are so outside the mainstream of constitutional thought," Aron said. "His view is such a narrow view of the Constitution . . . that I think it might be very difficult for him to reach conclusions in conformity with the law of the land."