Judge Anthony M. Kennedy, expected to be named by President Reagan to fill the four-month-long vacancy on the Supreme Court, is a judicial conservative, but one whose approach to the law appears far less ideologically driven than that of Reagan's original nominee, Judge Robert H. Bork.

The contrast between the two appeals court judges is best illustrated by their decisions in two nearly identical cases, in which both reached the same result but arrived there in strikingly different ways.

Both judges were asked to decide whether the Constitution prohibits the Navy from firing homosexuals. Both upheld the Navy policy.

But Bork used the case to launch a broad, controversial, and much-noticed assault on the Supreme Court's reasoning in cases establishing a right to privacy -- including its 1973 abortion decision, Roe v. Wade -- and to sound a clarion call on the need for judicial restraint.

Kennedy, on the other hand, tackled the subject gingerly, noting "substantial academic comment" that the Constitution protects homosexual conduct, including writings by liberal Harvard Law School Prof. Laurence Tribe.

Citing Roe v. Wade without a hint of criticism, he conceded for the sake of argument "that some kinds of government regulation of private consensual homosexual behavior may face substantial constitutional challenge."

Athough Kennedy ultimately said the Navy rule was valid because of the "unique" needs of the military, he was careful to point out that "upholding the challenged regulations as constitutional is distinct from a statement that they are wise."

Two weeks ago, when Kennedy appeared on the verge of being nominated to replace retired Justice Lewis F. Powell Jr., conservative legal scholar Bruce Fein expressed what is likely to be the reaction of many conservatives to Kennedy.

"What this represents is the capitulation of the Reagan administration in trying to change the general direction not only of the Supreme Court but of the lower federal judiciary," he said. "They do not want . . . to provoke the same kind of debate about the role and the direction of the Supreme Court" as occurred with Bork.

Kennedy, he said, "is 75 percent there; {in} 25 percent of the cases he kind of strays away" from the conservative line. "He is not nearly as philosophically driven as say a Bork or someone I would like . . . midway between Powell and Bork." In addition, Fein said, Kennedy is "not an intellectual giant. I don't think he's going to write with a brilliant pen that's going to be very persuasive to other justices' chambers or to the lower courts."

Tribe, who reviewed Kennedy's opinions when Kennedy was expected to be named to the court last month after the Senate rejected Bork, said he found the 51-year-old judge "refreshingly moderate. He is impossible to identify with the far-right positions Judge Bork has taken on a number of issues. He seems to be more a genuine conservative and less an ideological crusader."

While Bork had spent years attacking the intellectual foundation of much of modern constitutional law, Tribe said, Kennedy, "rather than reaching out to destroy every right in sight, reaches out to understand the deeper constitutional values at stake."

That is not to say, however, that Kennedy is likely to be a liberal justice in Republican clothing -- or, in fact, anything less than a generally conservative vote on the closely divided court, a role much the same as that played by Powell.

If nominated and confirmed as the 104th justice in the nation's history, Kennedy would come to the court with an impressive roster of conservative rulings compiled during his 12 years of service as a judge on the 9th U.S. Circuit Court of Appeals.

For example, Kennedy's staunch law-and-order credentials -- an issue Reagan emphasized when he nominated Judge Douglas H. Ginsburg instead of Kennedy -- are demonstrated by his dissent in a 1983 case involving use of the exclusionary rule, which bars the use at trial of any evidence improperly obtained by the police. Kennedy urged that judges allow such evidence to be used if the police acted "in good faith."

"Whatever the merits of the exclusionary rule," Kennedy wrote, "its rigidities become compounded unacceptably when courts presume innocent conduct {by suspects} when the only common-sense explanation for it is ongoing criminal activity."

The Supreme Court adopted Kennedy's views a year later in this same case, U.S. v. Leon, creating for the first time a "good-faith" exception to the exclusionary rule. In an opinion earlier this year, Kennedy extended the good-faith exception to foreign searches.

In 1985, Kennedy overturned the first statewide "comparable worth" ruling, a lower court decision requiring Washington state to give male and female employes equal pay for jobs of equal worth. A union study had found that workers in male-dominated jobs were paid, on average, 20 percent more than workers in jobs held primarily by women.

"Neither law nor logic deems the free market a suspect enterprise," Kennedy wrote. The federal law prohibiting sex discrimination, he said, "does not obligate {Washington} to eliminate an economic inequality which it did not create."

In Chadha v. Immigration and Naturalization Service, Kennedy said that Congress' use of the one-house legislative veto was an unconstitutional infringement on the separation of powers. That ruling was later upheld by the Supreme Court.

"He is a judicial conservative but a thoughtful one, persuadable . . . not terribly result-oriented," said Judge Alex Kozinski, one of Kennedy's first law clerks and now his colleague on the 9th Circuit. "He is not primarily an academician," Kozinski said. "He tends to approach things on a less theoretical basis. I don't think he has worked out grand theories about the way the Constitution works; he just deals with cases one at a time."

Indeed, Kennedy has shown he is willing to reverse criminal convictions in situations in which a criminal's constitutional rights were violated, but he also has been disposed to uphold strict punishment where appropriate.

In a 1979 case, Kennedy overturned a conviction based on an illegal search of a car, saying that "the facts relied upon to support the stop of the . . . vehicle do not . . . constitute grounds for a reasonable suspicion of criminal activity."

And in a 1977 robbery case, Kennedy reversed a conviction after finding that one of the codefendants should have received a separate trial.

However, in a case this year, Kennedy upheld a sentence of life imprisonment without possibility of parole for a man convicted on drug charges. "The sentence is harsh, and may upon first consideration seem open to question, for Stewart is a 47-year-old father of six with no prior record of criminal activity," he said. "The trial court, however, did not ignore these considerations. Instead, it weighed them against evidence that Stewart continued his operation while free on bail, expanding its scope significantly; directed the operation from his jail cell after revocation of bail . . . and displayed no remorse for his crimes. Such factors having been considered, the sentence must stand."

He also recently upheld the imposition of the death penalty in a Nevada case.

Kennedy appears to share some of Bork's views on libel law. Earlier this year, he dismissed a libel suit brought against the former mayor of Santa Monica, Calif., Ruth Yannatta Goldway, by a German-born woman who opposed rent control. Goldway allegedly likened the woman, Ilse Koch, to "a well-known Nazi war criminal named Ilse Koch during World War II."

Although the statement was "nothing more than a vicious slur," Kennedy said, it was not libelous because it was an expression of opinion rather than fact.

"In this case, if the mayor chose to get in the gutter, the law simply leaves her there," he wrote. " . . . This is the precise sort of contest that society can endure without redress from the court. Base and malignant speech is not necessarily actionable."

Other Kennedy decisions could raise the hackles of liberals, however. For example, in 1976 he threw out a lawsuit by housing discrimination "testers" who alleged that real estate agents steered minority customers to housing in certain neighborhoods. He said the testers did not have standing to sue.

Ralph G. Neas, executive director of the Leadership Conference on Civil Rights, which led the fight against Bork, said yesterday that not enough is known about Kennedy at this stage for the group to take a position on Kennedy's nomination. "People had just started to take a look at him" when Ginsburg was chosen, Neas said.