Vietnamese expatriate David Truong acknowledged yesterday that he knew that at least seven of the State Department cables he is accused of funneling to Communist diplomats in Paris were marked classified.

But Truong, son of a former Vietnamese presidential candidate, maintained that all of the cables contained information that was well known and none could be considered confidential.

One secret cable contained information that had been the subject of a congressional hearing. Truong said during his second day on the witness stand at his trial on espionage charges.

Truong is accused of spying for the Communist Vietnamese government along with former U.S. Information Agency official Ronald L. Humphrey. Both men have pleaded innocent to the charges in a trial which yesterday entered its 10th day in U.S. District Court in Alexandria.

Truong insisted that the cables failed to contain new information, despite their classifications. "Did any of these cables give you any news?" his defense attorney, Marvin D. Miller, asked at one point. "This? Truong responded, holding up a document. "No sir."

The 32-year-old Truong said yesterday that he sent the documents in question to some Vietnamese friends in Paris to help them publish a newsletter for the Vietnamese community there. Truong helped publish a similar newsletter in Washington, where he was well known as a Capitol Hill lobbyist for Vietnamese causes.

Humphrey earlier had testified that he removed classification markings from some State Department documents that he is charged with stealing from the U.S.I.A. for Truong. Yesterday Truong said he couldn't tell if the cables were from a news wire service teletype or other sources.

Although, he said five classified documents were found in his Washington apartment by the FBI, Truong said he believed the cables had been declassified. He said he had learned from other sources the information in the cables.

Defense attorneys in the case have contended that the documents named in the government's indictment against the two men are improperly classified and they are little more than "diplomatic chit-chat."

Truong said he never directed that the documents be given to the Vietnamese embassy in Paris. He said he was never paid by anyone in Vietnam for passing information; he has no friends in Hanoi, and that he never asked Humphrey to give him classified information. Humphrey never discussed the classification of the documents, Truong said.

When Truong gave the packages of cables and books to a courier to be sent to Paris he said he never tried to conceal their content and he used no special code or wrapping.

Truong said that when the packages were flown to Paris with the courier he figured they would be checked at by French customs officials, Court testimony had that the courier turned out to be a souble-agent paid by the U.S. Central Intelligence Agency.

"I would get them (the documents) in a hodgepodge of a whole bunch of items," including wire service stories and other public reports from Humphrey, Truong said.

One cable "dealt with prisoners of war and missing in action rumonrs and some xomments of a UPI reporter on Bangkok," Truong testified.

"Were you aware of the information before reading the cable" asked Marvin A. Truong's lawyer.

"Yes," Truong replied, talking directly to juurors. "Two or three weeks before I went to a House subcommitee hearing. An American testified to the same story. From what he heard there were POWs left in North Vietnam."

Truong said the cable was marked "secret."

"Did you think it was classsified at the time you received it?" Miller asked.

"No. This deals with information that's already out in the open," Truong responded.

Miller asked Truong if he knew four classified cables he sent to Paris in June 1977 were still classified when he sent them. Truong replied, "No."

Another cable discussed Vietnam refugees. Truong said he had already talked to refugees and read accounts of their plight in news stories.

Assistant U.S. Attorney Justin W. Williams spent more than two hours challenging Truong's defenses. When Williams asked Truong why he kept five classified documents in his apartment, Truong replied "No particular reason."

Williams asked Truong why he had books on spying and CIA Agents. Truong said he enjoyed reading them and ehudsed them in his lobbying work. The prosecutor also asked Truong why he never kept copies of the documents he is accused of sending to Paris. "No particular reason," Truong said.

Williams claimed that some of the cables involved in the case had nothing to do with Truong's avowed aim of helping the U.S. and Vietnam develop normal relationships.

One such cable discussed Russian miliatry advisors in Vientiane, Laos, Williams said. "What does that have to do with normalizing relations with Vietnam?" the prosecutor asked. "Nothing, sir," Truong answered.

Another cable was title "the Ethiopian request for arms" and Williams asked if it had anything to do with relations between the U.S. and Vietnam. "No, sir!" Truong said.

"Well, did you ever ask for (Socialist Republic of Vietnam) material to give to the U.S.?" Williams asked at one point.

"No, sir!" Troung answered loudly.