Secret Service agents told a federal judge here yesterday that they routinely erased a key tape recording and burned notes from interviews with witnesses about a violent attack last January on the Chinese chancery even though a criminal case is pending in the incident.

Defense lawyers for five members of the Revolutionary Communist Party, who are charged in the attack and have claimed credit for it, told U.S. District Court Judge June L. Green that the Secret Service's destruction of the evidence is crucial to their case and thus the charges should be dropped.

Assistant U.S. Attorney William H. Collins Jr., however, aruged that the missing evidence can largely be reconstructed through testimony and that the case should continue against the five U.S. supporters of the late Chairman Mao Tse-tung.

The judge said she would rule this morning.

Robert Banocy, deputy chief of the Secret Service's foreign mission branch, testified that the tape of officer Joseph Toriskie's call for help immediately after the Jan. 24 attack was erased 30 days later, in accordance with what was then standard Secret Service practice.

"In this case it was oversight," Banocy testified. "It didn't come to our attention that there was going to be a need for it."

Banocy said that since then Secret Service regulations have been changed and that tapes of radio transmissions are kept for 90 days or longer if some tape might be needed in a court case.

Secret Service agent Richard Bert later testified that two weeks ago he placed in a "burn bag" notes of interviews he held after the incident with Toriskie and two other witnesses, Charlie Denegal and a Chinese chancery staff member, Cheng Li-Sheng.

Bert told the judge he did not think he would be called as a witness in the case since he was not the arresting officer.

Defense lawyers Russell Canan and Stephen Bright also contended that the charges against the defendants should be dismissed because the Chinese have refused to waive diplomatic immunity to allow Cheng to testify in the case. But Green said the lawyers didn't "show any prejudice whatsoever" to the defendants and denied the motion.

The five men charged with destruction of foreign property and assault on a federal officer (Toriskie) are James J. Nelson, Gregory T. Ford, Curtis J. Mohn, James E. Loudermilk and Mark W. Jackson. They are attempting to portray their trial as political in nature, while the government views the trial as a case of vandalism.

The five smashed windows and splashed white paint across the front of the Chinese chancery at 2300 Connecticut Ave. NW to protest the visit a few days later of Chinese Vice Premier Deng Xiaoping.

While the five deny the assault charge on Toriskie, Loudermilk added, "Everything we did we're proud of."

Added Jackson: "What they consider to be vandalism was a political statement."

If Green denies the motion to dismiss the charges, testimony is expected to begin today.