President Reagan's latest nominee for the Federal Trade Commission yesterday was accused of using his position as a staff member on a Senate investigating committee to further his own financial interests.

Martin Steinberg, former chief counsel for the committee, testified at the confirmation hearing of F. Keith Adkinson that Adkinson repeatedly helped the interests of Gary Bowdach, a convicted felon who was serving as a subcomittee witness, after Adkinson signed a contract with Bowdach to write a book about organized crime.

Adkinson, a Washington attorney and former director of Democrats for Reagan in last year's elections, was employed as an investigator on the committee's majority staff at the time, said Steinberg, who now is minority counsel to the committee.

Steinberg testified that, at Adkinson's recommendation, Sen. Sam Nunn (D-Ga.), then chairman of the subcommittee, had been helping Bowdach--who had provided extensive testimony to the committee about organized crime--by writing letters to a federal judge, a parole board and to the Justice Department on Bowdach's behalf.

The matter was referred to the Justice Department's Public Integrity section, and Senate officials were told in May 1981 that the charges were dismissed, close to two years later.

Adkinson's role in the presidential campaign raised questions among the committee's Democrats about his true party affiliation--concerns that have been overshadowed by an apparently intensifying committee probe of the nominee's past. The committee is seeking access to Justice Department records about the matter and may interview Bowdach, who has a new identity as part of a witness protection program.

"The record clearly shows that you took repeated actions and made repeated recomendations which were clearly in Mr. Bowdach's interests" and "in the long run your own personal interests," charged Sen. Howard Cannon (D-Nev.), the committee's ranking minority member. But Sen. Robert Kasten (R-Wisc.), chairman of the consumer subcommittee, said he still supports the nomination.

Adkinson, 37, denied that the book and movie deal about Bowdach was pending while he worked on the Bowdach case. Adkinson said the deal for a 50-50 profits split was called off in January 1979, after he wrote drafts of one chapter that he said the two men felt was inadquate.

Adkinson said he entered the deal because Bowdach's story was a way to illustrate his concerns about the criminal system. But he said that with hindsight the contract might have been a mistake and he said that he did not believe at the time that he was violating Senate regulations which require the disclosure of outside compensation. Adkinson said he received none and therefore was not obligated to let the Senate know of the contract.