Supreme Court nominee Douglas H. Ginsburg said in a statement released yesterday that he had smoked marijuana "once as a student in the 1960s and on a few occasions in the '70s," acknowledging that it was a "mistake."

Ginsburg, a 41-year-old federal appeals court judge nominated by President Reagan last week to fill the vacancy on the court created by the retirement of Lewis F. Powell Jr., said "that was the only drug I ever used. I have not used it since."

The administration said publicly that it still supported the nomination. But the disclosure, which followed inquiries Wednesday morning by The Washington Post, appeared to trouble conservative Republicans expected to be in the forefront of Ginsburg's support. Some minimized the statement, but others said it would present problems for his confirmation.

Attorney General Edwin Meese III, who pushed for Ginsburg's nomination with the president after the Senate's rejection of Judge Robert H. Bork, the administration's first choice to fill Powell's seat, said in a statement late yesterday that "I applaud Judge Ginsburg for his forthright statement. As he states, his action, taken during his younger days, was a mistake. It certainly does not affect his qualifications to sit on the court today, and he should be confirmed expeditiously."

A senior White House official said Reagan was briefed yesterday morning by White House chief of staff Howard H. Baker Jr. about the situation. "The president still has confidence in him," the official said.

Another official said the drug use "obviously was a source of concern. What happens now is up to Ginsburg," that official said, adding "it's not clear yet what impact this will have, if any, on the nomination." That official pointed out that Ginsburg was "Meese's choice."

Sources who knew Ginsburg during the late 1970s when he was a professor at Harvard Law School said in interviews this week that Ginsburg, like others in his generation, used marijuana occasionally at social gatherings in Cambridge. These sources said they had no knowledge of his using any other drug or that he ever sold marijuana.

Ginsburg, in his statement, said: "Earlier today I was asked whether I had ever used drugs. To the best of my recollection, once as a college student in the '60s and on a few occasions in the '70s I used marijuana. That was the only drug I ever used. I have not used it since. It was a mistake, and I regret it."

A source close to Ginsburg said yesterday that Ginsburg had told administration officials that he had "never bought it, never owned it," and that he had used it "no more than a half-dozen times total ever in his life."

One former law school colleague, however, said that Ginsburg at one point had a small quantity of marijuana at his home and said that his total use amounted to more than six times.

Under Massachusetts law, possession of marijuana is, and was in the late 1970s, a misdemeanor punishable by imprisonment of up to six months, a fine of up to $500 or both, according to the state attorney general's office. The law, a spokesman for the office said, requires that first-time offenders "be placed on probation," and that upon successful completion of that probation the case against them be dismissed.

When asked Wednesday morning about the allegations, Justice Department spokesman Terry Eastland laughed and said, "I can tell you now that it is irrelevant."

Yesterday, Ginsburg, joined by Meese, met with Minority Leader Robert J. Dole (R-Kan.) and other Senate Republicans to apprise them of his use of marijuana and the possibility of news stories about it. Dole read Ginsburg's and Meese's statements on the Senate floor shortly after the announcement and added, "That statement, in my view, says it all."

Other reaction followed quickly. "I think all of us wish he hadn't done it," said Sen. Jesse Helms (R-N.C.). But he added that "the more relevant thing is that he assured us he hasn't touched it {marijuana} since then" and "there are more important things to discuss." Asked if he was bothered that Ginsburg had broken the law, Helms said, "I suspect that everyone on the high court has broken one law or another."

Sen. James A. McClure (R-Idaho), chairman of the conservative Senate Republican Steering Committee, said, "At first I thought, 'Oh it can't be true' but it was." He said the disclosure "certainly makes a difference" and could affect his vote, as well as Ginsburg's prospects for confirmation. "If it had been known before he was nominated, he would not have been nominated," McClure said. It might be accepted by some as a youthful indiscretion but "I'm not sure that's really sufficient," he said.

Sen. Orrin G. Hatch (R-Utah), who was among Bork's strongest defenders on the Judiciary Committee, said "it was a mistake; he acknowledged it . . . . Frankly, I'm not very concerned about it." He said he thought some people, including conservatives, "may very well be upset" but added, "I believe in the power of repentance and forgiveness."

Sen. Warren B. Rudman (R-N.H.) was among those most skeptical about Ginsburg's prospects. "It certainly doesn't help," he said. "I think in light of some of the disclosures {about Ginsburg}, they {the administration} are going to have to give serious consideration as to whether they have a major problem." Rudman said he thought there was "a problem from day one" with the nomination.

"The one thing this administration doesn't need now is another fight," Rudman added.

Sen. Strom Thurmond (R-S.C.), ranking Republican on the Judiciary Committee, said he did not "know enough about the facts" to comment and added, "I want to be fair to him."

Reagan overruled the recommendations of his White House staff in picking Ginsburg over Judge Anthony M. Kennedy, a more moderate federal appeals court judge in Sacramento. In announcing the nomination, Reagan said Ginsburg would be a law-and-order jurist, "a man who profoundly believes in the rule of law." In a nationwide radio address on Oct. 31, Reagan said "too many judges . . . made law enforcement a game in which clever lawyers try to find ways to trip up the police."

Drug enforcement has been one of the Reagan administration's most-publicized goals. First Lady Nancy Reagan has made it a personal cause, leading a campaign against drug use and urging youngsters to "just say no," and Meese, as attorney general, has made it a top priority of the Justice Department. Reagan's senior drug adviser, Dr. Donald MacDonald, asked Reagan last month to approve arresting not only drug peddlers but users of even small quantities of illegal drugs.

Applicants for high federal jobs are frequently asked about drug use. Ginsburg has undergone several background investigations by the FBI for his jobs at Justice, the Office of Management and Budget and the appeals court, but sources said no indications of prior drug use had surfaced.

FBI spokesman Lane Bonner said yesterday that generally a background investigation, which includes interviews of friends, colleagues and employers, "covers the use of illegal drugs and alcohol abuse and that would be reported to the White House."

But it was not known whether Ginsburg himself had ever been asked specifically about drug use when he was appointed to the federal appeals court here last year. A White House questionnaire asks job-seekers to "please provide other information which you regard as pertinent or which could be the possible source of embarrassment to you, or to the president, if publicly known."

For the last several years, lawyers applying for jobs at the Justice Department have been required to fill out detailed forms asking whether they had ever taken illegal drugs in college, law school, or any other time, and if so, what kind and how many times, attorneys said.

When the Justice Department began the policy of posing the questions, top department officials discouraged hiring applicants who acknowledged ever having taken drugs, according to sources in the department.

But Eastland said that the current policy in hiring decisions is based on a "common sense standard" about what types of drugs were used, and how long ago.

Sources said that some U.S. attorneys around the nation have complained to Meese's office that the department was losing the services of many talented young attorneys by being too strict in enforcing the policy. One Justice source said that a top Meese aide responded to at least one U.S. attorney that the hiring standard should be strict.

Yesterday's disclosure follows reports that Ginsburg may have acted improperly when he took a role in matters involving cable television while he owned nearly $140,000 in stock in a cable-TV company. A House committee chairman also has said that Ginsburg has not satisfactorily explained destruction of documents by the Justice Department's antitrust division, which he headed in 1985 and 1986.

From the moment Reagan nominated Ginsburg, his confirmation prospects were seen as clouded by his relative youth and inexperience and by the fact that the American Bar Association's judicial evaluations committee ranked him barely qualified last year for his appeals court seat.

Senate Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) said yesterday, before Ginsburg's announcement, that he hopes to begin hearings on the nomination during the week of Dec. 7, prompting complaints from Republicans that the hearings could and should be started earlier.

GOP members also reiterated that the ABA should speed up its review of Ginsburg, and there were protests from a Democratic as well as a Republican senator that the ABA ratings' importance is exaggerated by the Senate in considering judicial nominees.

Staff writers Lou Cannon, Helen Dewar, John Mintz and Mary Thornton contributed to this report.