Rep. Ronald V. Dellums (D.-Calif.) yesterday denied allegations that he has bought and used drugs.

Dellums, who is being investigated by a House committee and a federal grand jury for possible purchase and use of cocaine and marijuana, said in a brief statement late yesterday outside his Capitol Hill office: "I am aware of vague allegations which have been directed at us. I flatly deny them and have retained legal counsel for two reasons. One is to get the specifics of these allegations, who said what, what we were supposed to have done, and when we were supposed to have done them."

He said the second reason he retained Washington attorney Michael E. Tigar to represent him is so that he can continue to represent his constituents "unencumbered by these kinds of distractions."

Dellums declined to take questions from reporters.

Tigar, who appeared with him, told reporters that Dellums learned Tuesday from the House ethics committee that the congressman and his staff are under investigation for drug use.

Tigar said the House inquiry was required under House rules even when the evidence is "incredible and totally unworthy of belief."

Tigar said yesterday that allegations that Dellums bought drugs are false and that there is "no evidence" that any Dellums aides had ever been involved in any illegal activity. "That is a flat denial," Tigar said.

Tigar said he will meet today with Joseph A. Califano Jr., head of a special task force investigating allegations of congressional drug use for the ethics committee, and said he will meet later with D. Lowell Jensen, head of the criminal division at Justice, which also is investigating possible drug use on Capitol Hill.

Tigar said Dellums has received "no formal notification" from the Justice Department that it is investigating him for alleged drug use. Informed sources have told The Washington Post that a federal grand jury has heard allegations from a former House employe that Dellums anmd his staff bought and used marijuana and cocaine. The employe said he sold drugs directly to Dellums and to at least one of his staff members.

According to these sources, the employee, Robert Yesh, pleaded guilty in federal court here two weeks ago to two misdemeanor drug charges. Information about that pleading is under court seal.

Dellums is the third congressman whose name has been mentioned since the Justice Department and the House ethics committee began their investigations last July.

Federal investigators also have heard allegations of drug use by Rep. Charles Wilson (D-Tex.) and former representative Barry Goldwater Jr. (R-Calif.) according to sources familiar with the investigation. Both men have denied wrongdoing and no charges have been filed.

Knowledgeable sources said yesterday that the investigation into allegations of drug use by Goldwater, although technically still open, is for the most part over.

Those sources said that the Justice Department lawyer working directly on the case, Kurt W. Muellenberg, had recommended to superiors in the department that no charges be brought against Goldwater.

It was not known yesterday when the investigations against Wilson would be completed.