In a confused wrangle testing Zimbabwean justice, a member of Parliament was acquitted today of plotting to overthrow the government, was immediately re-detained by police and then freed six hours later.

Until the release late this afternoon of Wallace Stuttaford, of the all-white Republican Front party led by former prime minister Ian Smith, it appeared that he could once more be headed for lengthy imprisonment. Stuttaford already had served 308 days, most of that time under emergency regulations allowing detention without trial.

The police superintendent who detained Stuttaford today told him and reporters that he was doing so under orders from the minister of home affairs, Herbert Ushewokunze. The minister later issued a statement saying reports that Stuttaford "had been re-detained were inaccurate" and that he returned to Chikurubi prison "for purely administrative reasons."

It could not be learned whether Prime Minister Robert Mugabe ordered Ushewokunze to release Stuttaford, but an official in the premier's office said Mugabe and the home affairs minister had "communications" during the day.

Mugabe intervened two months ago and had two white farmers released in a similar case in which Ushewokunze twice ordered them re-detained after they were acquitted.

The confusing day of legal maneuvering came amid increasing concern by human rights activists and Western embassies over allegations of arbitrary detentions and torture by police, security and military officials. Zimbabwe is the former British colony of Rhodesia.

A Western diplomat, speaking before Stuttaford's release, criticized the detention, saying, "It is so inept to run your affairs that way. It's not going to do Zimbabwe's reputation any good."

Stuttaford is the most prominent person to be tried on charges of plotting against the Mugabe government, which came to power in 1980 after elections for black-majority rule that ended Smith's power. About 70 others, most of them blacks supporting opposition leader Joshua Nkomo, are scheduled to be brought to court in coming months.

Stuttaford was acquitted today when the government withdrew its case after the prosecutor disavowed the testimony of his key witness.

In court yesterday, the witness, Stanley Malumisa, failed to corroborate the statement he gave to security officials implying that Stuttaford, in conversations with him last year, spoke of using force to block Mugabe's plans to form a one-party state. "That statement was not given willingly and voluntarily but under wallops," Malumisa testified. "I should be a dead man by now . . . I gave it under torture."

Prosecutor Andrew Chigovera told Judge Enoch Dumbutshena today that "the state is left with no alternative but to withdraw the case against the accused" because of "the incredible and wholly unexpected nature" of that testimony.

Judge Dumbutshena said the prosecution's decision to drop the case was "well taken" and "in the interests of justice."

Stuttaford, 62, kept his emotions under control but his wife and sister sitting behind him broke into tears. He said he was looking forward to resuming his seat in Parliament.

Then, when they left the court and police Superintendent Sam Muchemwa told Stuttaford he was under detention, the women broke into tears again.

Stuttaford told his wife to "cheer up." Muchemwa said he was taking Stuttaford to central police headquarters but he was eventually taken to Chikurubi maximum-security prison, octagonal with 12-foot barbed-wire fencing. When he reemerged this afternoon, he said only that his "treatment was good . . . by prison standards."

His lawyer, Richard Wadman, added: "I don't think we'll ever say anything about the case." Two lawyers for imprisoned Air Force officers were recently threatened with detention after they told reporters that their clients had been tortured.

The British Foreign Office has expressed "very serious concern" over the detention of 17 Air Force officers, some of whom are British nationals, and the alleged torture of some of them. They are being held in connection with the sabotage of 13 planes in July. A British envoy attended the Stuttaford trial today.