Mayor Marion Barry said yesterday that D.C. officials have identified an 8-year-old heroin addict whom they believe was the subject of Sunday's Washington Post article about junevile drug abuse, but that the boy and his mother have "gone into hiding" to avoid being taken into custody.

The mayor said the boy had been identified through a drug-abuse counselor and psychiatrist at Howard University who has known the family for some time. The mother called the psychiatrist, Dr. Allyce Gullatte, yesterday and said she and the child had "left home . . . because she doesn't want to be arrested or have the child taken away from her," Barry said.

Barry's statement came after city police let pass a 10 a.m. deadline set earlier for The Washington Post to identify and help locate the child or face a possible subpoena for the reporter who wrote the story and for any Post editors with information on the child.

"I don't need The Washington Post to tell me where he (the child) is . . . we already know," Barry said during an afternoon press conference. The mayor rebuked Police Chief Burtell M. Jefferson, who, along with several police officials, had talked of the subpoena on several occasions late Monday and early Tuesday.

"You have not heard Marion Barry say he is going to subpoena anyone," the mayor said, adding that Jefferson had never contacted him before talking about the subpoena, which could have forced a legal showdown over constitutional guarantees of freedom of the press.

Yesterday afternoon, Jefferson and a departmental lawyer met for about an hour with Charles F. C. Ruff, the U.S. attorney here. After the meeting, Ruff said, "I support them in their effort to find out where the child is. I am concerned about the child's welfare; it should be the concern of everyone, including The Washington Post."

Ruff refused to comment on any details of his meeting with the police chief, but said, "No subpoena has been issued. No request for the issuance of a subpoena has been made." Ruff added that Justice Department regulations require any subpoena for journalists to be issued directly by U.S. Attorney General Benjamin R. Civiletti.

Barry said that Dr. Gullatte was trying to reestablish contact with the mother and child and to have them come in for treatment and counseling.

Jefferson announced at a press conference yesterday that the parent or anyone with information about the child could call either the police hotline, 393-2222, or the child abuse section of the Department of Human Services, 827-0995.

Early yesterday afternoon, Alan F. Grip, the mayor's spokesman, told reporters that city officials had actually visited a house in which they believed the family lived. "We had the address, but when we got there the people were gone," Grip said. "We are not giving out the address."

Later, however, Grip said he did not know whether police, city social workers or anyone had visited the house.

The mayor's announcement on the identification of the child appeared to be the first concrete advance since the story of the boy, identified in the story only as "Jimmy," was told on Sunday by Post staff writer Janet Cooke.

The article related how the boy first became acquainted with heroin, through sniffing it, at the age of five, and how he was now regularly injected with the drug, in some instances by his mother's boyfriend.

The article and a subsequent account of police efforts to locate the boy addict's family have provoked widespread concern in the city.

Callers to The Washington Post and others who telephoned a morning talk show on radio station WRC seemed to be rather evenly divided. Some felt that The Post should reveal its confidential information, while others criticized the police for doing an inadequate job.

A common thread running through much of this reaction was that the case of "Jimmy" was just one of thousands of child addiction problems in Washington.

Jefferson told reporters that his primary concern was for the physical welfare of the child.

Police again refused yesterday to say how many persons were involved in the search, although some sources said that about a half-dozen different neighborhoods were being checked.

The question of whether the newspaper should reveal the name or location of the boy had become a major issue throughout the city, as D.C. officials raised concerns that the child's life could be in increasing danger.

"We're going to do everything we can to get that information and save that child's life. We'll see how much The Post is willing to do to protect its First Amendment rights at the expense of that child's life," police spokesman Gary Hankins told a radio audience yesterday morning.

The Post's lawyer, John B. Kuhns of Williams & Connolly, said yesterday, "The enormous public response to this article reflects the serious concern of the community about drug use, particularly by our youth. No article about this boy's tragic circumstances would have been possible if The Post could not protect the confidentiality of its news sources.

"Although the immediate pressures to reveal sources in a single case are often intense, such disclosure would gravely jeopardize The Post's ability to report on this and other issues of vital concern to the community," Kuhns said. "The Post's decision to protect the confidentiality of its sources is essential if it is to continue to fulfill its constitutional function of informing the public."

After the meeting with Ruff, however, police officials appeared to be moving to defuse the issue. Asked yesterday afternoon what he planned to do about the newspaper, Jefferson replied, "That's secondary. I won't even deal with that. Our primary concern is to locate the youngster."

Barry said yesterday that he believed the reporter was breaking the law by not disclosing the information. "The problem you run into," Barry said, "is that it is illegal for anybody, even a reporter, to observe a crime and not report it."

Asked if he thought the reporter who wrote the article had broken the law, the mayor replied, "I think so."

Several legal sources said yesterday, however, that merely observing criminal conduct is not a violation of law.

Police, meanwhile, continued yesterday to talk with informants, principals and schoolchildren in their effort to find the child. Deputy Chief James Kelly of the 7th District in Southeast, responding to questions of how a reporter could find the child and the police be unable to, said, "It's not that easy. We're the last people anybody wants to talk to.'"

Narcotics officials said they are questioning addicts who may have gone to the child's home to buy drugs or even shoot up, in the hope that one of those persons who might later want a favor from the police, would agree to give information about the family.

Deputy Chief Theodore R. Carr of the 6th District in Northeast and Southeast Washington, said, "It seems to me there is a lot of emotion surrounding this kid, and there should be. However, there is still the huge drug use in the city that has to be dealt with. Once we find this kid, the problem will not be over."