Attorney General Benjamin R. Civiletti yesterday concluded his inquiry into allegations that White House chief of staff Hamilton Jordan used cocaine, and there were strong indications he had decided against appointing a special prosecutor.

Spokesmen for Civiletti and the special prosecutor's division of the U.s. Court of Appeals to which he submitted his decision declined comment. But a government source said Civiletti had relied on an FBI investigation which produced little more than "conjecture, speculation and third-party hearsay statements."

The source said he understood the attorney general had concluded that pursuing the allegations further would be unjustified.

Civiletti was said to have asked the three-judge court to release a summary of his report, detailing his reasoning. George Fisher, the Court of Appeals clerk, said there would be no statement before tomorrow.

The preliminary inquiry, ordered by Civiletti in August, dealt with two allegations. One, made by lawyers for Steven Rubell and Ian Schrager, co-owners of Studio 54, a New York discotheque, alleged that Jordan had been seen using cocaine in 1978 at the nightclub.

Rubell and Schrager pleaded guilty Nov. 2 to charges of federal tax evasion after they failed to set up a deal under which the tax charges would be dropped if they dropped their allegation against Jordan.

The other allegation charged that Jordan used cocaine at a Beverly Hills party Oct. 21, 1977, while in Southern California for a dinner to raise funds for the Democratic Party.

That charge was made by Lana Jean Rawls, a Texas woman, who subsequently softened the allegation. She finally said that Jordan's friend, John Golden, gave her $500 to purchase cocaine and that she had only "circumstantial evidence" that Jordan had used the drug.

A Department of Justice inquiry is required by the Ethics in Government Act whenever a serious allegation is made against any of about 100 government officials covered by the statute. The Jordan case was complicated by the fact that Rawls and other potential witnesses sought immunity from prosecution in return for their testimony.

Department officials were troubled by whether they could grant immunity during the 90-day preliminary inquiry stage or whether they had to leave that to a special prosecutor. Neither Rawls nor two other potential witnesses were granted immunity that officials said they had sought.

That problem was said to have been resolved for the Jordan case by the lack of any substantial evidence supporting the allegations against the White House aide. However, one source conceded Wednesday that the question of whether immunity can be granted while deciding if a special prosecutor should be appointed could prove to be troublesome in the future.