The Supreme Court yesterday left standing a ruling by Idaho judges that public officials can force newspapers and reporters to reveal confidential news sources simply by suing them for libel.

The justices refused - without comment - to review a 3-to-2 Idaho Supreme Court decision requiring the Lewiston Morning Tribune and reporter James E. (Jay) Shelldy to identify a source even though the public official had shown neither a compelling need to know nor malice on the part of the defendant.

Shelldt, a special correspondent of The Washington Post, said in Lewiston that he expects to go to jail within two weeks to serve a 30-day sentence that was stayed pending Supreme Court action.

The trial judge imposed the sentence, for contempt of court after Shelldy cited the constitutional guarantee of a free press and a professional ethics in refusing an order to identify the source.

In Washington, the Reporters Commitee for Freedom of the Press, a legal defense and research fund, said that at least in Idaho, a newspaper is now "absolutely naked and defenseless" against anyone who wants to file a libel suit in order to identify a confidential source, "regardless of how careful a newspaper was.

The committee's executive director Jack C. Landau, also said that the lower court ruling although limited to Idaho, will encourage public official around the country "to file libel suits to find out who the sources were on a story."

Shelldy, recently promoted to executive editor of the Morning Tribune, said that an Idaho judge in Twin Falls already has relied on the ruling to order two reporters for the Times-News there to identify everyone they talked to for a story in which all sources were named.

The reporters refused to comply. Last week, the judge struck the papers' and the reporters' defense, thus leaving them in default in a $16 million libel suit brought by an insurance company. Shelldy, said, The Times-News is appealing to the Idaho Supreme Court.

The Morning Tribune case began in August 1972, when Michael A. Caldero and another undercover agent for the Idaho Bureau of Narcotics and Organized Crime went to a public park in Coeur d' Alene to arrest a man named George Booth. Dale Johnson , who had driven Booth ot the park tried to flee. Caldero shot Johnson three times.

Johnson, backed by two eyewitnesses, said the Caldero, dressed as a "hippie," did not identify himself as a police officer before shooting. Caldero said Johnson had tried to run him down.

More than two years later, Shelledy learned of the shoting while preparing a six-part series on the narcotics unit. Coeur d'Alene police merely had said in a statement that a shooting had occured during a drug arrest.

In an article on Nov. 23, 1973, Shelledy, who had interviewed a dozen persons about the episode, quoted Idaho Attorney General W. Anthony Park as saying that Caldero had fired after getting "a little shook up" and that the shooting was a "mistake."

The article also cited a confidential source - described as a "police expert" - who said that Caldero's account, in Shelledy's words, "didn't add up."

The series was highly critical of the narcotics unit. So were later reprots by, among others the federal Law Enforcement Assistance Administration. As a result of the reports, the state fired Caldero and several top agents.

In late 1974, Caldero sued the Morning Tribune for libel, claiming that the article was false, defamatory and malicious. In pre-trial proceedings, Caldero asked Shelledy to name the police expert and added him as a defendant when the reporter refused. Judge Roy Masman then imposed the jail sentence, which the newspaper appealed.

The Morning Tribune, hoping to persuade Caldero to be interviewed, had offered to show him the disputed article and has delayed publication of it for two weeks.

Until now the Supreme Court had not indicated that it would allow a litigant in a civil proceeding to compel disclosure of confidential sources. It had ruled in 1972 that in a criminal proceeding a reporter could not refuse to divulge to a grand jury information in his possession relating to his observation of the commission of a crime.

In the Idaho Supreme Court, the majority ruled on the 1972 decision, Branzburg vs Hayes to rule for Caldero.

One dissenter protested that Caldero had made "no showing" that he had tried to learn the police expert's name "by alternative means less destructive to First Amendment freedoms . . . Moreover, Caldero has not even come close to establishing the critical importance of Shelledy's testimony."

The other dissenter said that the press has a qualified priviledge to protect news sources in which the First Amendment-protection of newsgathering can be denied only if outweighed by the need of a ligitant to discover material information. Caldero had not shown such a need and the article about him was neither false nor defamatory, the judge said.