The Central Intelligence Agency has confirmed in court documents something government officials have long denied: that Ellsworth Bunker, when he was ambassador to South Vietnam, offered to finance the campaign of an opposition candidate in the Vietnamese presidential election in 1971.

The revelation - based on tape recordings - is contained in a CIA memo quoted from during a pretrial deposition in the civil suit against former CIA officer Frank Snepp.

Snepp wrote that Bunker offered Gen. Duong Van Minh $3 million as a bribe to keep him in the race as token opposition to incumbent Nguyen Van Thieu "for appearances' sake." Minh withdrew from the campaign, however.

The White House "flatly denied" earlier reports of the transaction and Bunker also has been quoted as denying the reports.

But in the deposition of CIA officer Norman Jones, a Justice Department attorney read from a CIA document: "Blank listened to the tapes, blank, in which Ambassador Bunker offered to finance, blank, race for the presidency. Blank noted that the amount of $3 million was not mentioned in the conversation, although the basic report by Snepp is true." (Blanks are the CIA's deletions.)

Bunker, now ambassador-at-large at the State Department, and CIA officials declined comment yesterday on the agency's confirmation of the financial offer to Minh or the taping of the conversation, which took place in Minh's home.

Snepp, who is being sued because he refused to submit his book for review by the agency, said in a phone interview yesterday that "$3 million" probably wasn't mentioned the conversation because "the pitch was made in piasters (Vietnamese currency) not dollars."

Snepp also said he was not surprised to learn the meeting between Bunker and Minh had been taped. "There could have been a bug in his home, or Bunker or his aide might have been carrying a recorder in a briefcase. They tried that once with Ky (Vice President Nguyen Cao Ky) but it didn't work."

It has been disclosed that the United States "bugged" Thieu's presidential palace during the war.

Minh, a retired general who stay in Vietnam when Thieu's regime was defeated by the North Vietnamese in the spring of 1975, was urged to run against Thieu in the 1971 election, sources said at the time, because the United States wanted to ensure a genuine contest.

Bunker allegedly made the offer of aid to Minh after returning from a trip to Washington in August, 1971.

Snepp said he first heard rumors of the $3 million offer during an early tour as a CIA officer in Saigon. His book, Decent Interval, is highly critical of the American withdrawal from Vietnam.