The bribery and conspiracy trial of Rep. Daniel J. Flood was reassigned to U.S. District Court Judge Oliver Gasch yesterday after Judge Louis F. Oberdorfer disqualified himself because he had brief dealings with the Pennsylvania Democrat in a 1964 tax investigation.

"Such an important and sensitive case ought to be conducted as nearly free as possible from side issues which might attract additional pre-trial publicity," Oberdorfer said in a memorandum disqualifying himself.

Oberdorfer set Jan. 15 as the trial date for the colorful and powerful Flood, but Gasch could alter that date after familiarizing himself with teh case.

Oberdorfer said that, when he was assistant attorney general heading the Justice Department's tax division in 1964, Flood called him on behalf of constituents who were being investigated.

The judge said that an assistant of his had already decided not to criminally prosecute the case on Sept. 9. 1964, 12 days before Flood called him. However, the taxpayers and their attorneys had not yet been notified.

Oberdorfer said his review of that case and conference with both sides in the current Flood case had led him to conclude that "my impartiality could not reasonably be questioned so as to justify disqualifying myself."

But Oberdorfer said he agreed with government attorneys that he could not now publicly release the documents in the 1964 tax case because of provisions of the Privacy Act and the Freedom of Information Act.

As a result, the judge said he concluded "that it would not be appropriate for me to try such an important and sensitive case unless those (1964) memoranda were in the public record."