Fugitive financier Robert L. Vesco, who has tried to implicate White House aides in an alleged bribery plot, failed in almost seven hours of questioning Sunday to produce "a smoking gun" for two members of the Senate Judiciary Committee.

Calling Vesco "one of the best con men that I've come across," Sen. Dennis DeConcini (D-Ariz.) said that Vesco provided no corroboration for either old or new allegations, including one about Billy Carter.

In a series of news conferences after his return yesterday fom Nassau, Vesco's refuge in the Bahamas, DeConcini said that Vesco claimed to have "orchestrated" the arrangement paid $220,000 to the president's brother as partial payment on what Billy Carter says was a $500,000 loan.

Billy Carter was unaware of the orchestration, DeConcini said Vesco told him. Vesco's stated purpose in involving Billy Carter was to wreak "vengeance" on the Carter administration for refusing to lift criminal charges pending against him.

DeConcini said he had "no reason to believe" Vesco's orchestration claim. "It's not credible because it comes from Mr. Vesco," he said. "I don't trust him," he added. Moreover, he said, he believed Vesco was "trying his best to use" him and Sen. Orrin G. Hatch (R-Utah) "to implicate this administration."

DeConcini is chairman and Hatch a member of a Senate Judiciary subcommittee that has been authorized to investigate purported links between Vesco and White House aides and associates of the president.

DeConcini said that Vesco failed to produce coroborative evidence on the grounds that he wanted to retain "control of the investigation." DeConcini, saying he could not yield control, said he has no intent to issue a large number of subpoenas or hold hearings. By contrast, Hatch told reporters at National Airport that the possible investigation could be one of the most important in history.

Earlier, columnist Jack Anderson accompanied Hatch and three Senate aides to Nassau for a three-day round of talks with Vesco. Also in the entourage was Frederick A. Cain, a polygraph expert brought along by Anderson to administer a lie detector test to Vesco. Before taking the best, DeConcini said, Vesco was allowed to read and change the questions.

"I did not approve of the lie detector test or the manner in which it was given," said DeConcini, a former prosecutor.