Six white Air Force officers were acquitted today of charges that they plotted to blow up 13 Zimbabwean airplanes last year, but they were immediately rearrested and returned to prison.

The move appeared certain to exacerbate tensions between the black-ruled government of Prime Minister Robert Mugabe and the white minority here, as well as worsen relations with the United States and Great Britain, Zimbabwe's two largest donors of foreign aid.

The six senior officers, jailed for the last 13 months, were acquitted by a judge who ruled that their confessions, the main evidence against them, were obtained through torture, beatings and intimidation. Judge Enoch Dumbutshena, the first black judge appointed by the newly independent government in 1980, also ruled that the defendants had been improperly denied access to their lawyers until after their confessions, which the six officers later repudiated.

They were permitted about 20 minutes with their relatives in the courtroom before being taken to a basement room where, they were told, they would receive their release papers.

But once downstairs, a dozen police officers filled the room, and each of the officers was presented with papers signed by Home Affairs Minister Herbert Ushewokunze that redetained them indefinitely. They were then handcuffed. On the way back to a holding cell, they were led past a crowd of stunned and tearful relatives and supporters, some of whom shouted "black bastards" at the police.

The six were rearrested under the Emergency Powers Act, inherited from the former white-minority government of Ian Smith. It empowers officials to imprison indefinitely and without trial any persons considered a threat to state security.

Under the law, the government has seven days to issue a formal statement of reasons for the redetentions. Ushewokunze's written orders today said only that "it appears to be expedient in the interests of public safety and public order" to redetain the officers.

Both Ushewokunze and Mugabe had given strong indications in recent interviews that the officers would be rearrested if they were acquitted for what Mugabe called "technical reasons." Mugabe had hinted that, despite police misconduct in obtaining the confessions, evidence had convinced him that the officers had abetted the airplane sabotage. Nine jet planes were destroyed and four others sustained major damage in the explosion on July 25, 1982, at the Thornhill Air Base in central Zimbabwe.

The state charged the six officers, all of whom had served in the former Rhodesian Air Force, with plotting the explosion and helping three unidentified saboteurs from South Africa commit the act and escape across the border.

Nearly half the Air Force's combat strength was destroyed or damaged, at a cost of nearly $9 million.

The case attracted international attention when five of the officers, all of whom pleaded not guilty, charged that last August and September police had tortured them by electric shock or beaten them into confessing.

All six were shuttled among various police stations in an effort to keep them from seeing their attorneys until after the confessions.

The judge said that he found the defendants' accounts "credible," and he called testimony from some prosecution witnesses "more than suspect."

The officers now join 49 other persons, whom the government says it has detained indefinitely as threats to state security. Other independent sources, including some church organizations, contend that there are several hundred detainees, most of whom are in the Matabeleland region, where the Army launched a crackdown on dissidents earlier this year.

Both American and British diplomats had entreated government officials privately in recent weeks to allow the officers to go free if acquitted. The United States has provided more than $200 million in aid in the years since independence, and Britain has given $180 million. Diplomats are known to fear that future aid allocations could be adversely affected by the redetentions.

Four of the Air Force officers hold dual Zimbabwean-British citizenship, and British Prime Minister Margaret Thatcher is expected to strongly condemn today's action.

The redetentions also could cast a cloud over Mugabe's official visit to Washington in two weeks.

Diplomats here expressed hope that the redetenions are temporary steps to give officials time to review the cases, and that at least some of the officers might be released soon.

Harry Ognall, the British attorney who led the officers' defense, said that their supporters would "apply pressure [for their release] at the highest levels" here, in London and in Washington.