Senate Democrats harshly criticized the Reagan administration yesterday for appointing few women and minorities to the federal bench, rejecting administration explanations that it has tried but cannot find suitable candidates from those groups.

Sen. Edward M. Kennedy (D-Mass.) said the administration, which has named 367 nominees to federal courts, selected only six blacks and 31 women, numbers that Kennedy said showed the administration was trying to turn the federal judiciary into an "exclusive club" open only to white men.

But Stephen J. Markman, an assistant attorney general in charge of the Office of Legal Policy, said the administration had made every effort to find qualified women and minorities but that the pool of acceptable candidates from those groups was small.

"We would love to find more qualified black and minority candidates," said Markman, who handles judicial selection for the administration. But, he said, only 3 percent of all lawyers are black, most are Democrats and a great number are too young to become federal judges, having graduated from law school only in the last decade or so.

Neither side expected yesterday's hearing to produce any change in the administration's policies in making appointments to the 761-member federal judiciary. The administration likely has only a few more months to get any nominees confirmed by the Democratic-controlled Senate in this election year.

But sources involved in the selection process said the Justice Department and the White House are mindful of the criticisms in weighing a replacement for departing Judge Robert H. Bork on the influential U.S. Court of Appeals here, and Markman said yesterday that women and blacks were under consideration for that seat.

Kennedy held up a Senate vote on former assistant U.S. attorney Royce C. Lamberth's nomination to the U.S. District Court here for almost five months, demanding that Attorney General Edwin Meese III testify at an oversight hearing on the administration's record on appointing women and minorities. Kennedy ultimately settled for Markman, who he said yesterday "did a good job defending the indefensible."

Kennedy said Reagan had not fulfilled his campaign pledge in 1980 "to seek out women to appoint to other federal courts to bring about a better balance on the federal bench."

Kennedy said the administration's policy was most evident in the District of Columbia, where "every single one of the 14 persons this administration has nominated to the federal bench in Washington is a white male." It is, Kennedy said, a record "particularly unacceptable" given the large number of women and minority lawyers in firms or government service here.

Markman said federal courts here were national, not local courts, and that despite criticism by Senate Democrats and the D.C. Bar, "it would be entirely inappropriate for the administration to allow a local bar association to monopolize any proportion" of federal court vacancies.

He added that "the administration has viewed racial, gender, ethnic or religious group memberships as irrelevant" in making appointments. "The process is open to individuals without regard to these considerations." But Markman said the administration has not attempted "to ensure the nomination of particular proportions of individuals" from particular groups.

The administration's record, Kennedy argued in nearly two hours of sparing with Markman, was "getting worse," not better, even as the number of women and minority lawyers with substantial experience was rapidly increasing. He cited figures indicating a drop last year in the percentage of women and minorities nominated from the average in the first six years of the Reagan administration.

The administration from 1981 to 1986 nominated 293 judges, of which 27 or 9.2 percent were women, 5 or 1.7 percent were black and 13 or 4.4 percent were Hispanic. In 1987-88, Kennedy said, 5.4 percent of the administration's 74 nominees were women, 1.4 percent were black and 1.4 percent were Hispanic.

The number of women and minority lawyers with substantial experience has increased sharply in the last 15 years, Kennedy said, "but you are appointing less." Kennedy, citing testimony from minority and women's law groups, said the reason was that the "administration has made no real effort to look."

Markman insisted that "this administration has appointed more women and minorities and in greater percentages than any other administration" except President Jimmy Carter's -- even though more than 90 percent of blacks are "strongly identified" with the Democratic Party, and "political realities" are such that the party in the White House has always overwhelmingly picked candidates with similar political views.

There was "no evidence of bad faith" or a "scintilla of evidence" that the administration was rejecting candidates on the basis of race or sex, he said.

Markman said he "welcomes names" of candidates from women's and minority bar associations, and keeps an "open door" to those groups.

Had Reagan ever named someone recommended by those groups or withdrawn anyone based on criticism from those groups, Kennedy asked.

Markman said he did not think that had happened.

Sen. Patrick J. Leahy (D-Vt.) said Meese, at his confirmation hearings in January 1985, promised the committee that he would recommend appointment of more women and minorities but Markman's testimony "is at odds with what {Meese} told us when he was seeking our votes for confirmation."

Markman said the administration tried "to sweep the net in as broad a way as we possibly can," but that "it is going to take several additional years" before the pool of experienced women and minority lawyers would be large enough to permit more appointments from those groups.