John B. Clyburn and Roy Littlejohn, D.C. contractors and political allies of Mayor Marion Barry, acknowledge giving money to Karen K. Johnson, but both men contend their actions had nothing to do with Johnson's refusal to testify before a federal grand jury investigating allegations of drug use by the mayor, according to knowledgeable sources.

Sources said Clyburn contends he gave Johnson money and channeled additional funds from Littlejohn to her out of sympathy for her financial plight after she was imprisoned for a year on cocaine charges and for refusing to testify.

Both men say they did not give Johnson any money or indicate any willingness to give her money until after she had decided not to testify and the grand jury had ended its investigation, according to the sources.

The accounts of Clyburn and Littlejohn, as described by sources, directly contradict what Johnson, 35, is believed to have told federal prosecutors in numerous meetings during the past two months.

Sources said that Johnson, who agreed to cooperate after prosecutors promised her she would not be charged, has told prosecutors that she received $20,000 to $25,000 in return for not testifying in 1983 and 1984. Johnson has said she received some of the alleged hush money from Clyburn directly and that she believes Littlejohn also contributed funds to buy her silence, the sources said.

Littlejohn and Clyburn are prominent District contractors who have received millions of dollars in city business. Barry has denied any knowledge of the alleged payments to Johnson, with whom he acknowledged having had a personal relationship from 1980 through 1982. He has also said he has had no contact with Johnson for 4 1/2 years and has denied ever buying or using cocaine.

The Washington Post has learned that Johnson alleged to prosecutors that her former attorney, John A. Shorter, negotiated or brokered the payments to her and kept a substantial portion of the money in compensation for his legal services. Shorter, formerly a politically well-connected lawyer here, is serving a 40-month sentence for income tax evasion at a federal prison in Montgomery, Ala.

Allan N. Palmer, Shorter's lawyer, said yesterday, "As far as we are concerned, these allegations are strictly uncorroborated rumors without any basis in fact."

The exact nature of the alleged hush money agreement is unclear, but sources said Johnson has told prosecutors she was led to believe that she would not have to worry about her financial well-being if she were jailed for refusing to testify.

Sources said Johnson told prosecutors she picked up some payments at the K Street offices of Clyburn's company, Decisions Information Systems Corp. FBI agents also witnessed what they believe was an alleged payment to Johnson at the tennis courts of the Omni Shoreham Hotel on Calvert Street in Northwest Washington, where Clyburn and other associates of Barry often play tennis, sources said.

Johnson has said she accepted the money in installments that usually amounted to $200 or $300, with no payment exceeding $1,000 at a time, sources have said.

Prosecutors have been able to corroborate some of Johnson's statements through her brother, Jared Kinnon, sources have said. Kinnon has told prosecutors he collected some of the money for Johnson while she was in jail, according to the sources. He has testified before a grand jury under a grant of immunity, the sources said.

Prosecutors also are examining Johnson's financial records, which were seized from her house May 22, for evidence of payments.

Johnson's refusal to testify in 1983 and 1984 stymied a federal investigation into alleged cocaine use by Barry and others. Prosecutors intended to question her then about a secretly taped conversation in which she said she had sold cocaine to Barry on 20 to 30 occasions.

Her cooperation was considered crucial to prosecutors' attempts to determine whether Barry committed perjury when he told the grand jury that he never bought drugs from Johnson.

Johnson was jailed in August 1984 on a contempt of court charge and remained there for eight months until the term of the grand jury investigating the allegations ended. She then served four months in a halfway house for possession and sale of cocaine.

Accounts given by Clyburn and Littlejohn differ substantially from what Johnson has told prosecutors on the timing, purpose and amount of the payments.

The sources said Clyburn and Littlejohn deny giving Johnson any money while she was in jail on the contempt charge. In addition, Clyburn estimates that he gave Johnson far less than the $20,000 to $25,000 figure she has given to prosecutors, sources said.

Clyburn also denies that he contributed any money to pay Johnson's legal bills from Shorter, according to sources.

Sources said Clyburn became friends with Johnson after meeting her at a party that Barry also attended.

Littlejohn gave Clyburn money for Johnson at Clyburn's request, but did not have any personal contact with Johnson, according to sources.

According to this account, Clyburn described Johnson to Littlejohn as a friend in need and Littlejohn contributed the money out of sympathy.

Clyburn and Littlejohn deny that they committed themselves to help Johnson over any period of time, though Clyburn says he told Johnson that he would try to help her if she continued to experience financial difficulty, the sources said.

Asked to comment on Clyburn and Littlejohn's accounts, G. Allen Dale, an attorney for Johnson, said, "It's a shame there aren't more people like Mr. Clyburn and Mr. Littlejohn. The experience I've had with people is that they don't give away money just for the heck of giving away money."

Thomas Dyson, Clyburn's attorney, said, "No hush money was paid by John Clyburn or anyone else to my knowledge."

Eugene M. Propper, Littlejohn's attorney, also said "the allegation that Littlejohn paid hush money is false."