Syndicated columnist Jack Anderson said yesterday that the key evidence he used to link two top presidential advisers with fugitive financier Robert Vesco was not authentic.

In a column distributed for use today, Anderson said his sources now claim they lost, and then "reconstructed" from memory, letters implicating presidential aide Hamilton Jordan and scheme to fix Vesco's legal problems.

Meanwhile, Kirbo offered reporters the results of his own intensive investigation which he said shows the documents to be false. Kirbo said he has hotel records, plane logs and comparisons of typewritten letters that he says rebut the Anderson allegations.

Anderson said in a phone interview that his new findings "weaken badly" the authenticity of the critical documentation on which he based his original columns.

But the columnist refused to concede that the key evidence may have been totally manufactured by R. L. Herring, an Albany. Ga., businessman who dealt with Vesco. "My sources insist that they [the documents] were not fabrications, but reconstructions," Anderson said.

The letters were re-created about Aug. 1 in Panama City, Fla., by Herring, his brother and brother-in-law and their wives. Anderson reported his sources said. He did not say in his latest column that this was one week after Herring was indicted on federal fraud and racketeering charges.

Anderson revised his original column linking Jordan and Kirbo to an attempted Vesco "political fix." But even the softer version was greeted by heated denials by Jordan, President Carter's closet White House aide, and Kirbo, the Atlanta attorney who is another confidant.

Kirbo even started his own investigation into the matter and said his research showed Herring and his associates were not even in Georgia on the dates the damaging letters allegedly were written.

Kirbo suggested yesterday in a phone interview that Anderson's own reexamination of the documents was spurred because "he probably found out what we've done in our own investigation."

Anderson said he discovered the reconstructed documents last week when he received more material from his Georgia sources and became suspicious about one of the papers.

"We went back to our sources and subjected them to sharp cross-examination," he said. "One of the wives finally broke down. She said they [the document] were all authentic, but were reconstructed because some of the originals were missing."

Anderson said that his sources told him phone messages that mention calls from Jordan were "copied over" from originals that were too dim to read. The originals were then thrown away, the columnist reported his sources said.

Anderson's finding raise questions about the sworn testimony of Gerolyn Hobbs, Herring's former secretary, who said she remembered typing and mailing the letters and writing the phones messages.

"We'd have never used the letters and other documents if she hadn't authenticated them," Anderson said.

"And she claims she took part in no reconstruction."

He quoted Hobbs in his new column as saying the letters "are similar to the ones I typed."

"I did the best I could to authenticate documents," Anderson said. In his first column, he said that "independent sources" including Hobbs "have attested to their authenticity."

Meanwhile yesterday, Kirbo disclosed details of his own investigation into the documents. It showed "clear as a bell," he said, that many of them were false.

After checking plane logs and hotel records, Kirbo found that Herring and his associates were not in Albany, Ga., at the time Anderson contended they sat in Herring's Albany ofice writing the incriminating letters.

They were either in Costa Rica or airborne on the way to or from Costa Rica at the time, Kirbo said.

Kirbo also found gross discrepancies between the letters in question and other, unrelated letters typed by the same secretary in the same office. Formats were different, signatures were different and the typing was different, Kirbo said.

For example, on the unrelated, routine business letters, Herring's secretary put her initials after her boss's initials, as is the standard form. On the incriminating letters to Jordan and Kirbo, her initials appear first.

"Any number of things were different," said Chet Tisdale, a Kirbo associate. The same secretary who typed the routine letters in a "competent and efficient" manner violated all the rules of business letterwriting in the Kirbo-Jordan letters, he said.

"It wasn't even a gray area," said Kirbo. The discrepancies "were clear as a bell."

Herring went on trial yesterday for the unrelated fraud and racketeering charges growing out his dealings in the coal industry.

Spencer Lee IV, the boyhood friend of Jordan, who Herring hired to approach the Carter administration, has testified that Herring told him he was making a case to discredit the Carter administration.

The Justice Department has been conducting an investigation into the allegations that Herring and Lee tried to influence administration treatment of Vesco's legal problems.

Vesco fled to Costa Rica and more recently to the Bahamas to escape U.S. charges that he looted a large conglomerate and then tried to buy his way out of trouble with a $200,000 gift to the Nixon campaign in 1972.

Anderson said yesterday that his sources have agreed to talk with the FBI about the "reconstructed" documents.

Clearing up the authenticity of the alleged letters and messages about Jordan and Kirbo, however, still will not explain the note the White House said President Carter sent Attorney General Griffin B. Bell last year after being told by an aide about the Vesco plan.

Lee has acknowledged he came to Washington last February to approach Jordan on Vesco's behalf. But he has testified he backed out of the deal on the advice of another Georgia friend and White House aide, Richard Harden.

The White House disclosed last week that Harden told President Carter that Lee would get "a large sum of money" to arrange a meeting with Jordan for Vesco representatives.

But the only action Carter took was to send a cryptic hand-written note to Bell saying: "Please see Spencer Lee from Albany when he requests an appointment."

That was the first announcement that Carter hadbeen informed about the Georgia group's efforts. The White House had not given any indication in early briefings on the controversy that Carter was aware of the Vesco case.

Press secretary Jody Powell said the administration had not been asked that specific question. But he added the answer then would have been "no" because Harden didn't mention his meeting with the president until after Anderson's first column appeared.