The District of Columbia City Council gave narrow, preliminary approval yesterday to legislation that would decriminalize possession of small amounts of marijuana.

The legislation would neither legalize possession of marijuana nor lower existing penalties for sellers. It would, however, treat possession of 1 ounce or less of the drug in much the same way as parking violations now are handled.

Yesterday's Council action, in which a narrow 7-6 majority defeated crippling amendments to the bill, does not constitute final action. A final vote is tentatively scheduled

City Baptist ministers opposed to Oct. 25. the bill and marijuana lobbyists in favor of it were present during two hours of emotional debate on the matter yesterday.

"This law would protect first-time offenders from carrying criminal records for the rest of their lives," said David A. Clarke (D-one), chief sponsor of the bill. "Without it, if an employer looks at a person's record and sees a violation of a narcotics law, he's not going to ask whether it was for heroin or what."

"To me, this legislation is morally and ethically wrong, and I shall teach that it's wrong both in and out of the Council," said Jerry A. Moore (R-at large), a Baptist minister.

Under the legislation, a person apprehended for possessing one ounce or less of marijuana would receive a citation similar to a parking ticket and could be fined as much as $100 for each of the first three offenses. After the third violation, possession no longer would be decriminalized and offenders would be subject to the same maximum penalty of a $1,000 fine and a year in jail that is set forth in city law.

In addition, the legislation would remove the stigma of a criminal record for the first three violations. Records, kept separately from criminal files, would note each violation.

At present, persons arrested for possession of marijuana are charged under the comprehensive Dangerous Drug Act of 1938, which also covers heroin, cocaine and other hard drug offenses. Criminal records do not now indicate which drug an offender is accused of possessing.

Last summer, President Carter also spoke in favor of decriminalizing possession of small amounts of marijuana for personal use.

Some Council members said they opposed the decriminalization legislation because they believe it will lead to greater use of the drug.

"Here we say that it's illegal to smoke the substance, but we are going to just give citations," said Council member Willie Hardy (D-seven).

"I have problems with that kind of shenanigans. This bill would mean that we are permiting a person to break the law three times, and I won't go for it," she said.

Council member Wilhelmina Rolark (D-eight) argued. "This bill is not just wrist-slapping. Lt would treat people the same way that they are being treated now.

"What I am concerned about is that many of those that are caught are black youths and, when it comes time for them to seek jobs, it's going to be increasingly difficult for them to get hired and we already have extremely high unemployment," Rolark said.

Her statement in favor of the legislation brought a visible sigh of relief from Keith Stroup, national director of the National Organization for the Reform of Marijuana Laws (NORML), a group that has lobbied for the past seven years here and elsewhere for decriminalization.

Stroup said that he had not been certain that Mrs. Rolark would cast the decisive seventh vote for the bill until she spoke.

Two years ago, a similar marijuana decriminalization bill gained tentative approval in the Council but was allowed to die after intense lobbying by the city's committee of 100 ministers.

At that time, Mayor Walter E. Washington said he opposed such legislation. The mayor has not commented on the new bill. Nine votes are needed to override a veto.

When the bill was considered two years ago, City Council Chairman Sterling Tucker (D) voted for it. Yesterday he voted against the new bill after what one Council source said was intensive lobbying by the Committee of 100.

The source also said that Tucker, who is considering running for mayor next year, may be seeking to win the support of the ministers who claim to have a following of about 100,000 people.

Before the meeting yesterday, Tucker lobbied several Councl members to vote to table the legislation, an act that many considered an effort to ditch the bill.

"I talked to Chairman Tucker many times about how we feel on this legislation, and we are difinitely opposed to it," said the Rev. Andrew Fowler, a spokesman of the Committee of 100. In the audience with Fowler yesterday were about six other ministers, most of them members of the committee.

"Last time we held prayer meetings to oppose the bill, and I can't say for certain what our strategy is this time, but we will continue to hold public prayer meetings and oppose this anyway we can," Fowler said.

Fowler said he also has talked to the mayor about his opposition to the bill but has not asked the mayor to veto it.

"I don't know what the mayor is going to do," Fowler said. "He has always voted on the side of morality, but if the people ask him to vote for it, he might."

Those who voted in favor of the legislation were Clark, John A. Wilson (D-two), Polly Shackleton (D-three), Arrington Dixon (D-four), Marion Barry (D-at large), Rolark and Hilda Mason (D-at large).

Those against it were Hardy, Jerry Moore, Douglas Moore (D-at large), Tucker, Nadine P. Winter (D-six) and William Spaulding (D-five).