The nomination of F. Keith Adkinson, national director of Democrats for Reagan in the 1980 campaign, to a Democratic seat on the Federal Trade Commission, is threatened by charges that he acted improperly while he was a Senate staff member, sources said yesterday.

In 1979, Sen. Sam Nunn (D-Ga.), chairman of the Senate permanent subcommittee on investigations, forced Adkinson to resign from the staff after he learned that the aide had signed a book contract with a committee witness and failed to disclose it as the subcommittee's leadership felt he should have under Senate rules.

A Justice Department investigation cleared Adkinson at the time, but the Senate Commerce Committee is restudying the episode as it weighs his nomination. Sources said it appears that all of the committee's Democratic members are prepared to vote against the nomination. FTC observers see the appointment as an important one, because the current four commission members are expected to divide their votes evenly on many issues.

The controversy over Adkinson arose after he and the witness, Gary Bowdach, convicted of racketeering charges, signed a contract in December, 1978, for a book about Bowdach's life, including his participation in the government's witness protection program.

Adkinson wrote a chapter for the book in January, 1979, but did not notify his superiors of the contract until August that year. In a signed statement, he said that profits from the book and related projects would be split equally between the two men. However, he said none of the work would go forward until he left the subcommittee.

Adkinson has told investigators that because no money changed hands, he was not required to disclose the contract to the Senate on May 15, when Senate rules require employes to report outside activities involving compensation. But that did not satisfy the subcommittee's leadership which asked him to resign. Adkinson has since abandoned the book project.

Congressional investigators are also evaluating charges raised in the confidential FBI check on Adkinson's nomination that after the book contract was signed, Adkinson continued to work on committee business involving Bowdach. In fact, at the recommendation of committee staff, Nunn pushed for Bowdach's release from prison.

Bowdach was released in December, 1978, but was returned to prison in 1979. Nunn again sought his release on the advice of his staff, which still included Bowdach. Nunn has refused to comment, as has Adkinson, who said through an attorney that he would say nothing until his confirmation hearing.

Sen. Robert Kasten (R-Wis.), chairman of the Senate Commerce consumer subcommittee, agreed last week to postpone the committee hearing for a second time after Sen. Howard Cannon (D-Nev.), the committee's ranking minority member, could not attend. "From what I know I still support him," Kasten said last week. Another hearing is tentatively scheduled for Thursday.

Adkinson, now a labor lawyer with a Washington firm, was confronted with the charges and his political problems Thursday in a meeting with James A. Baker III, White House chief of staff. Adkinson said he would continue to seek the post and Baker said the administration would continue to support him.

In papers filed with the Senate Commerce Committee last month, Adkinson said that during the five years he worked for the subcommittee "there were instances when allegations of impropriety were made against" the panel's staff, including one instance when anonymous charges were made against him.

Adkinson said those allegations were "immediately referred" to Justice, which "dismissed" them after an investigation. Adkinson wrote that he had advised the White House of the charges before he was nominated on Oct. 19.

The Senate investigation began, in part, because some Senate Democrats felt they were not adequately consulted about the nomination. Adkinson is believed to be the first new Democratic appointment Reagan had made to a regulatory commission.

Senate Democrats have also questioned Adkinson's affiliation because of his campaign ties to Reagan.. Adkinson, however, says he has been a registered Democrat since 1966.