The Justice Department yesterday closed its 15-month investigation into allegations of drug use by members of Congress, saying it had not found sufficient evidence to bring charges against two congressmen and one former congressman who were the targets of the investigation.

In a letter to Joseph A. Califano Jr., special counsel to the House ethics committee, the department said it conducted a "complete investigation" of allegations against Reps. Ronald V. Dellums (D-Calif.) and Charles Wilson (D-Tex.) and former representative Barry Goldwater Jr. (R-Calif.) and "determined there is insufficient admissible, credible evidence to support criminal charges."

The department, in a brief statement, said that while it had decided not to file criminal charges, it believed information developed during the investigation would be relevant to the committee, which is conducting a parallel investigation of allegations of drug use on the Hill.

The department said it would be willing to furnish its information to the committee. Ethics committee Chairman Rep. Louis Stokes (D-Ohio) said yesterday he would not comment on the committee's investigation.

Dellums, Goldwater and Wilson have repeatedly denied using or buying drugs. All three hailed the department's announcement.

Dellums, in a statement released by his lawyer, Samuel Buffone, said he was "gratified that the Justice Department has further vindicated my innocence" and said he "looks forward to complete vindication" from the House ethics committee.

Goldwater, who told a reporter last month the lengthy investigation was "screwing up my life," said yesterday in a statement that he was "pleased by the Justice Department announcement that nothing will come of their investigation against me." He said that the last year "has been a difficult one for me and my family because of the unfounded rumors against me."

Goldwater, who now raises funds for a cancer research foundation, is not the subject of an ethics committee probe. Wilson said at a press conference he was "greatly relieved that it's over."

His lawyer said later that Wilson has been told unofficially that the ethics committee is conducting an informal preliminary inquiry into allegations against him, but he was "not concerned" about that inquiry, because of all the allegations he has heard, there is none that would be of interest to the ethics committee.

Wilson said he was "angry about the money this has cost me," which he estimated at up to $100,000 in legal defense and clerical costs, and "angry about the grief it caused" him and his family.

Wilson said he believed the department's investigation was based on "uncredible allegations" by a Texas man who pleaded guilty to wire and mail fraud last year. Wilson was among a group of investors swindled in a phony stock deal involving the man, according to authorities.

Wilson said he was angered by what he called the department's "double standard" in attempting to prosecute him for drug use. He said that if a private citizen had been accused of the same crime, the investigation would not have been a major one.

"That's what happened in Germany. They started using different standards for different classes of people," Wilson said.

Wilson said media coverage of the investigation generally had been fair but that NBC television had been "the villain" in describing him as the "number one target of a drug-ring investigation." He also said The Washington Post had been inaccurate. He did not elaborate, but his attorney said afterward he was referring to an initial account in The Post that incorrectly identified the source of the allegations against Wilson.

Dellums' accuser was Robert Yesh, a former employe of the House doorkeeper's office, who is serving a one-year prison sentence after pleading guilty to conspiracy and intent to distribute cocaine.

Sources said Dellums' aide and chauffeur, John Apperson, who was also accused by Yesh, denied Yesh's allegations in testimony before a grand jury earlier this month.

The Justice Department investigation began last April after the arrests of two Washington-area men on charges of distributing cocaine to an undercover D.C. policeman.

Both men, Troy M. Todd Jr., 23, of Potomac, and former Capitol Hill page Douglas W. Marshall, 27, of Northwest Washington, have pleaded guilty to charges of cocaine distribution.

A fourth man, former House doorkeeper's employe James Beattie, 27, of Alexandria, was sentenced last week to one year's probation after pleading guilty in May to possession and conspiracy to possess cocaine.

The U.S. attorney's office here is completing its investigation of drug allegations against House employes but there are no pending allegations against House members, the Justice Department said yesterday.