Rep. Charles Wilson (D-Texas) has spent much of the past six months fending off allegations that he used cocaine on three occasions with friends in 1980--charges being investigated as part of a Justice Department probe into Capitol Hill drug use--and he's getting pretty tired of it.

"It's absolutely astounding the lengths to which they the Justice Department have gone to try and figure out what I did in a hot tub in Las Vegas," Wilson said in an interview in his congressional office last week.

"If they had put the same resources into drug trafficking . . . there would be half as much heroin coming into the United States as there is now."

Wilson said he has never used cocaine or marijuana. Justice has found nothing to support the allegations against him, Wilson said, and yet has dragged out the investigation because he is a congressman.

Sources familiar with the Justice investigation said last week that the congressman's version of events has been corroborated by at least two witnesses and that the credibility of the man who was the original source of the allegations is questionable.

Justice sources said no decision has been made yet on whether to close the case and the investigation is continuing.

Wilson, a tall, lean and rugged-looking 49-year-old from Lufkin, Texas, has taken a much different, more aggressive stance than others who have been subjects of the year-old investigation. Wilson, first elected to Congress in 1972, has spoken openly about the allegations and his view of Justice's handling of them.

"The allegations were ignored and discredited," Wilson said, "and there was no interest in them until the attorney general decided that congressmen were going to be held by a different standard than the rest of the population."

Wilson and others associated with the investigation said the original source of the allegations is Paul Brown, a former friend of Wilson's who spent five months in federal prison in Texas last year after pleading guilty to one count of mail fraud in connection with charges that he swindled Wilson out of $29,000 in a phony stock deal. The judge ordered that Brown repay Wilson the money.

Attempts to reach Brown through his parole officer and his attorneys were unsuccessful.

Wilson said that one allegation that has been investigated is that he sniffed cocaine that someone gave him in a hotel suite in Las Vegas on a weekend in 1980. He explained that he and a woman friend and Brown and another man were in Las Vegas together that weekend. But Wilson said he was not in the room when cocaine was allegedly sniffed in a hot tub.

"I was not in the tub," he said. "I was asleep in the next room."

John D. Aldock, a lawyer for Wilson's female companion that weekend, Liz Wickersham, said neither he nor his client would comment on the investigation.

Sources close to the investigation said that Wickersham, a former model who now hosts a cable television talk show in Atlanta, has supported Wilson's version of events to Justice.

Wilson said another allegation that has been investigated is that the congressman used cocaine after that weekend as he rode in a limousine with Wickersham and Brown from Baltimore/Washington International Airport.

Wilson said Justice interviewed the chauffeur of the limousine and that the man said he was sure Wilson had not used cocaine in the car. Wilson said he knows the name of the chauffeur and his lawyer but declined to name either.

Sources close to the investigation said the chauffeur was interviewed and said no drug use had occurred in the car.

The Justice investigation into Capitol Hill drug use was sparked a year ago with the arrest of two Washington area men, Douglas W. Marshall and Troy M. Todd Jr., on charges of operating a cocaine distribution ring on the Hill. They were indicted last November on charges of conspiring to distribute cocaine on Capitol Hill between September 1978 and April 1982. The men were recently extradited from Australia and are awaiting trial in U.S. District Court in Washington. They have pleaded not guilty to the charges.

A special task force headed by Joseph A. Califano Jr. is conducting its own investigation, separate but parallel to the Justice probe, for the House ethics committee. If that investigation finds evidence of misconduct, the ethics committee could recommend disciplinary actions such as a reprimand or expulsion from the House. Wilson said the committee has not told him whether he is a subject of its investigation.

In addition to Wilson, Rep. Ronald Dellums (D-Calif.) and former Rep. Barry Goldwater Jr. (R-Calif.) have been under investigation by Justice for alleged drug use. All have denied the allegations, and no charges have been filed. Sources have said that Justice attorneys recommended months ago that the probe against Goldwater be dropped but that no final decision has been made.

The investigation against Dellums is continuing.

Wilson has not been publicly linked before with Marshall or Todd.

Wilson said in an interview last week that Marshall worked for him as a bartender five times in 1977 or 1978. In what he called the "worst piece of news I've had in the entire investigation," Wilson's wife, from whom he has been separated for several years, told him about two weeks ago that Marshall tended bar for them at four parties at their home and once in the congressman's office.

Wilson said that before his wife mentioned it, he was unaware that he had ever met Marshall, who was a House page.

The congressman said recalled a young bartender who came to his home, and that he seemed to be a nice young man who was particularly friendly and helpful at the parties. The bartending occurred before the time of the alleged drug conspiracy, Wilson said.

Marshall's lawyer, Christopher G. Hoge, said that his client is now at "a delicate stage of negotiations with the government" and that it would be inappropriate for him to comment about the case now.

Wilson said he resents what he called the double standard being used by Justice for congressmen compared to other citizens, who are not normally investigated for alleged personal use of small amounts of drugs. The investigators have interviewed a "couple dozen" of his friends, traveling to Houston, Las Vegas, Los Angeles, New York and Denver. Wilson said he has spent $30,000 so far in legal fees.

"That's one thing that's kind of made me furious about the press in this particular instance, because they haven't shown any irritation that there are 535 Americans out of 220 million Americans that should be investigated on hearsay evidence on occasional use," Wilson said.

"My point is that, innocent or guilty, I would not have been put through this hassle and had to spend this money if I were not a congressman."