Supreme Court nominee Anthony M. Kennedy ended his Senate Judiciary Committee testimony yesterday to the praise of Democratic leaders and with his confirmation virtually assured.

"I don't believe you are in any trouble," Senate Majority Leader Robert C. Byrd (D-W.Va.) told the 51-year-old federal appeals judge. "I'm inclined to vote for you barring any unforeseen happenings."

Committee Chairman Joseph R. Biden Jr. (D-Del.) said Kennedy "did not have any ideological briefs in your back pocket. You are an extremely honorable and open-minded" judge.

Their comments were in keeping with the subdued 12-hour questioning of the Sacramento jurist that was a sharp contrast to the more than 30 hours of often contentious questioning that President Reagan's original choice for the vacant court seat, appeals Judge Robert H. Bork, faced from the committee before it rejected his nomination. Justice Lewis F. Powell Jr. retired from the high court last summer.

In two days of hearings in the Senate Caucus Room, only conservative Sen. Gordon J. Humphrey (R-N.H.) expressed strong reservations. Both Republicans and Democrats asked Kennedy questions as if his confirmation were a foregone conclusion.

Some senators such as Sen. Strom Thurmond (R-S.C.), the ranking minority member, appeared to be rehearsing their endorsement speeches, telling Kennedy he had been an impressive witness. "We can all cut these questions short," Thurmond said. "The only conclusion that we can draw is that you're a good man and ought to be confirmed."

And committee liberals, who said they did not want to appear to be "beating up" on the low-key and affable candidate, used their time more to tell Kennedy how they hoped he would vote than to quiz him on his views.

Sen. Howard M. Metzenbaum (D-Ohio) began one series of questions saying: "I would hope that when you are on the court . . ." And Sen. Edward M. Kennedy (D-Mass.) said he was "looking for some assurance" that once on the court Kennedy would not use procedural barriers to "booby trap . . . those left out or those left behind" from "equal justice under the law."

Contributing to the laudatory atmosphere was a letter released by the committee from the American Bar Association's judicial evaluations committee explaining its unanimous decision to give Kennedy a top rating.

"This committee," the letter said, "is satisfied that its investigations reveal that Judge Kennedy's integrity is beyond reproach, that he enjoys justifiably a reputation for sound intellect and diligence in his judicial work."

The hearings are expected to conclude Thursday, but no vote on the nomination will be taken until after the Senate returns from its holiday recess in late January.

Throughout his appearance before the committee, Kennedy insisted he was not a rigid ideologue -- a characterization often voiced about Bork.

Instead, Kennedy portrayed himself as a pragmatist. "I do not offer myself as someone with a complete cosmology of the Constitution. I do not have a unitary theory of interpretation."

He called himself a judge who was still "searching . . . for the correct balance in constitutional interpretation."

Although Kennedy continued to answer most questions put to him, he declined to voice a general view about some of the most controversial issues before the high court, including affirmative action and the court's rulings on a right to privacy.

Asked specifically whether there was, as the high court said in 1965, a "marital right to privacy protected by the Constitution," Kennedy said, "Yes."

Kennedy said he had deep reservations about the liberal Warren Court's rulings in criminal law, which he said had sparked a "revolution" in that area, but he stopped far short of Attorney General Edwin Meese III's call for overturning some of those rulings, especially the 1966 Miranda ruling requiring police to warn suspects of their constitutional rights to remain silent and have a lawyer present during any questioning.

Kennedy yesterday said the Miranda decision was a "sweeping, sweeping rule. It is not clear to me that it followed directly from the words of the Constitution. It went to the verge of the law," he said, and "may have gone beyond the necessities of the case."

"But since it is established," he said, "it is entitled to great respect. I know of no strong argument to overturn it."