A federal magistrate, saying he hoped his action would "deter congressmen from dabbling in drugs even for social occasions," sentenced a former House employe to one year in prison yesterday for allegedly conspiring with Rep. Ronald V. Dellums (D-Calif.) and an aide to obtain cocaine and marijuana.

U.S. Magistrate Arthur L. Burnett also unsealed the record of a closed hearing March 9 that makes public for the first time a series of specific allegations involving Dellums, including one that Dellums on two occasions had obtained cocaine on the floor of the House.

Robert T. Yesh, a longtime employe in the House doorkeeper's office, pleaded guilty in that March 9 hearing to one count of conspiring with Dellums and his aide, John C. Apperson, and to one count of possession of cocaine.

No charges have been filed against Dellums or Apperson, both of whom deny any wrongdoing.

Law enforcement sources had acknowledged earlier that Dellums was one subject of an ongoing grand jury investigation into allegations of drug use on Capitol Hill, but Apperson's name had not been publicly mentioned until Burnett revealed it in court yesterday.

Both Dellums and Apperson have been notified that they are the subjects of a House ethics committee investigation that is proceeding separately but parallel to the federal inquiry.

In a statement released by his office yesterday, Dellums said that he had not previously been informed of any specifics of the allegations against him. Saying that Yesh has acknowledged that he is an alcoholic and that Yesh has had trouble with the law before, Dellums said: "I am deeply concerned that such serious allegations, based on apparently uncorroborated statements by an individual whose credibility must be questioned, have never been previously revealed to me."

Burnett, calling this the "most difficult sentence in my 10 years as a magistrate," said at a hearing yesterday that he sympathized with Yesh's problems but had to weigh "the interests of citizens in the integrity of Congress." He said he wondered why Yesh did not notify authorities "the very first time he was approached by Congressman Dellums," and that Yesh's case raised concerns about the extent of possible drug use by congressmen.

Burnett said that in sentencing Yesh, who faced a maximum two years in prison, he had to "take into account the interests of the citizens of Berkeley," Dellums' home district.

Noting that Yesh had said he obtained drugs from congressional pages working on the Hill, Burnett said Yesh "didn't try to stop those practices." The magistrate said he had to be "mindful . . . of the interests of young pages" in determining what sentence to impose.

Yesh has been cooperating with prosecutors conducting the grand jury inquiry and has taken lie detector tests administered both by the ethics committee and the Department of Justice. The results of those tests have not been made public.

Burnett said that "assuming the polygraph tests" Yesh took were accurate and that Yesh "passed 100 percent," he was obliged to send Yesh to prison with the hope that that action would "deter congressmen from dabbling in drugs even for social occasions."

Lawyers for Dellums and Apperson said Burnett's comments at the hearing could be prejudicial to their clients. "I think it is unfortunate that the judge decided to smear Mr. Apperson and ascribe credibility to a person like Yesh ," said Michael Kennedy, Apperson's lawyer. Kennedy said Apperson denies all the allegations.

Kennedy said yesterday he understood that Apperson was the only Dellums aide who is under investigation by the Justice Department and the ethics committee. A Dellums aide said other staff members have been questioned by ethics committee investigators, but that Dellums himself has not been questioned.

At the March 9 hearing, Assistant U.S. Attorney Daniel J. Bernstein told the court that if the case against Yesh went to trial, the government would prove that on a total of six occasions in 1980 and 1982 Yesh sold marijuana and cocaine to Dellums or to Apperson.

Samuel J. Buffone, one of Dellums' lawyers, said yesterday, "This is the first we've heard this" and complained that the Justice Department had not been willing even to confirm that Yesh was the source of allegations against Dellums.

Yesh is the first person to be sentenced to prison in the Justice Department's year-long investigation of alleged drug use by congressmen or Capitol Hill employes.

That investigation was sparked by the arrest and subsequent indictment last year of two Washington area men, Douglas W. Marshall and Troy M. Todd Jr., on charges of operating a cocaine distribution ring on the Hill. Both men were arrested in January in Australia and were extradited from there earlier this week. They are expected to be back in Washington on Sunday.

Prosecutors filed papers in court yesterday asking that bonds for Todd and Marshall be set at $1.5 million each. A bond hearing is scheduled for Monday in U.S. District Court.

In court yesterday, Bernstein called Yesh, who has testified before both the House committee and the federal grand jury, a "vital link" between the "Todd-Marshall conspiracy and the Hill."

At the March 9 hearing, Bernstein detailed the allegations the government would prove if the Yesh case went to trial. He told the court that:

In the spring or summer of 1980, Yesh and Dellums allegedly discussed smoking marijuana in a conversation in a snack bar in the Democratic Cloakroom of the House. Yesh told Dellums he could get him some marijuana for about $30 to $35 an ounce and Dellums told Yesh to bring him one bag, Bernstein alleged.

That afternoon, Apperson, who is a scheduler and chauffeur for the seven-term congressman, allegedly called Yesh, made arrangements to meet him that day and gave Yesh $30 or $35 in exchange for the marijuana. Yesh later asked Dellums if the marijuana was good and Dellums told him that it was, Bernstein said.

Bernstein said that one month to six weeks after that, Dellums approached Yesh on the floor of the House and asked for marijuana--"two bags, if available." Apperson once again met with Yesh and gave him money in exchange for the marijuana, the prosecutor alleged.

In the fall or winter of 1980, Yesh and Dellums allegedly had a conversation on the rail of the House floor in which Yesh asked Dellums if he was interested in buying cocaine. Bernstein said Dellums told Yesh to get one gram for him if he could. Bernstein said Yesh later, on the floor of the House, handed Dellums a plain white envelope with one gram of cocaine in it and Dellums paid him $100 a short time later saying, "Thanks for the loan."

Bernstein alleged that Dellums approached Yesh three weeks later and asked if he could get two grams of cocaine. Yesh got the drug and gave it to Apperson, who paid him $200 for it, the prosecutor said.

Bernstein alleged that on one occasion in the fall or winter of 1980 Yesh, Dellums and Apperson all snorted cocaine in a bathroom in Dellums' private office.

At some point after that alleged incident, Yesh was absent from his job for a substantial period of time between February 1981 and February 1982 after suffering two heart attacks, Bernstein said.

Shortly after Yesh returned to work, Dellums asked him about obtaining more drugs and Yesh subsequently sold one gram of cocaine to Dellums on the House floor for $100, Bernstein alleged. There was also one other occasion in February or March 1982 when Yesh allegedly sold cocaine to either Dellums or Apperson.

Bernstein also told Burnett at the March 9 hearing that Yesh's statements have been "corroborated in part by a tape of a conversation Yesh had with Apperson."