Seven months before he signed the prescription that led to his resignation from the White House yesterday, Dr. Peter G. Bourne publicly used two illegal drugs, cocaine and marijuana, at a party given for 600 people by the National Organization for the Reform of Marijuana Laws.

Bourne, who was then the president's chief adviser on health and drug abuse, inhaled cocaine into both nostrils through rolled up currency in a bedroom with about a dozen other persons, according to witnesses.

In an interview yesterday, Bourne denied that he has ever used cocaine. "I won't say that I've never used marijuana, but not since I've been on this job," he said. "It's just not my style I use alcohol."

Bourne was the president's chief adviser on health and drug abuse from the beginning of the Carter administration.

The incident last Dec. 10 was first reported yesterday by syndicated columnist Jack Anderson on ABC's Good Morning America show, and has been substantiated by a witness interviewed by The Washington Post.

According to the witness, Bourne made no attempt to hide his use of drugs at the NORML party,w which took place at a renovated town house in the 1700 block oof S St. NW.

"There was a mound of it (cocaine) about the size of a large prune being passed around on a glass with a razor blade inside it," the witness said. When the glass was passed to Bourne he used the blade to drawn out a small portion of the drug into a line and inhaled through the rolled dollar bill, the witness said.

Bourne was wearing a suit at the time and talked with many of the others in the party crowd of middle class students and professionals in their 20s and 30s, according to the source. At another point during the party, outside the bedroom, the person saw Bourne smoke from a marijuana cigarette and pass it on.

Gary Cohn, an investigative reporter for Anderson who developed their story, said yesterday that he has written statements from three wwitnesses who said they saw Bourne use thee drugs at the party.

These sources said they saw Bourne take "three or four hits" from the mound of cocaine, Cohn said. He said the bedroom was on an upper level of the house in an area roped off from the rest of the party.

Keith Stroup, national director of NORML, was reportedly in the room when Bourne used cocaine. Yesterday Stroup said he "wont't deny" that Bourne used the drugs and he said that the refusal to deny was "significant." But he declined to elaborate. "I don't feel comfortable commenting about private drug use by a public person or anyone else," Stroup said.

NORML, a lobby based in Washington, put on the party as part of its annual convention.

NORML's business manager, Mark Heutlinger, said the group tried to limit the number of partygoers to NORML, supporters but that many people brought friends.

Stroup acknowledged that marijuana was passed around freely at the party, and Heutlinger said he was "sure" cocaine was used "because, when you have a party with 600 people, it will be there."

In an interview yesterday, Stroup said of Bourne's leaving: "I do not see it with any great sadness." Stroup's relations with Bourne ahad been strained ever since a Bourne aide was splattered with a pie thrown, as "a political statement, I guess," during the NORML convention. Stroup said that he was wrongly blamed for the incident and that persons in Bourne's White House office suggested in letters to NORML officials that Stroup should be removed.

An article in New Times magazine, scheduled to be released next week, quotes Stroup as saying of the alleged pressure from Bourne's office: "This is the most heat I've felt in eight years running NORML. I had to go around the country explaining this."

The New Times article reports that Stroup then warned some of Bourne's aides that he might tell newspapers about the "recreational drug" preferences of White House aides.

In an interview with The Post yesterday, Stroup denied making such a threat, although he said he did repond to what he interpreted as unfounded criticism. "I told them that if they were going to play hardball they have no ability to define the territory," he said. "They all know they have vulnerabilities."

Stroup said Bourne later apologized for the pressure put on Stroup, which Bourne attributed to aide.

Charles O'Keefe, a staff aide in Bourne's office, last night labeled as "totally absurd" these absurd" these accounts of friction between NORML and the White House. "Why the hell should we care who is the president of NORML or any lobbying group?" he asked.

When Stroup was asked yesterday if he was aware of any "recreational drug use" in the White House, he declined to comment.

When Bourne was asked whether there was any "recreational drug use" by White House aides, he said, "Not by me."

Possession of marijuana or cocaine is a misdemeanor crime, punishable by a maximum $1,000 fine and a year in jail. Any further violation involving cocaine becomes a felony, with stiffer penalties. In practice, Washington police and prosecutors have been lenient in recent years in dealing with persons found to be in possession of small amounts of marijuana.