The leader of the Movement for Democratic Change, Morgan Tsvangirai, stopped short of threatening to boycott a runoff but said there was a mounting climate of fear.

Mr. Tsvangirai told a news conference: “In the runoff, violence will be the weapon. It is therefore unfair and unreasonable for President Mugabe to call a runoff.”

Tsvangirai’s party claims he won 50.3 percent of the vote in last weekend’s election, but official results have not been released. Independent projections show Tsvangirai won the most votes but not the 50 percent plus one needed for an outright victory.

His comments came after police officers prevented lawyers representing the opposition party, which claims to have won the national election on March 29, from entering Zimbabwe’s High Court on Saturday to file a lawsuit to force publication of official election results.

Even though Zimbabwe’s electoral commission has not released the result of the presidential vote, it was clear that Mr. Mugabe’s party had lost its majority in the lower house of Parliament for the first time since the country’s independence from white rule in 1980.

The ruling party was also trailing the opposition in the contest for the 60-seat Senate, by 20 to 23 seats, according to results released on Friday.

The slowness in announcing a presidential victor has led to deep suspicions of vote tampering and international criticism.

From its own tally of vote totals posted at each polling station, the opposition said that Mr. Tsvangirai eked out a bare majority. But while an independent projection of results by local democracy advocates put Mr. Tsvangirai well ahead of Mr. Mugabe, it was not by enough to avoid a second round of voting.

Legally, a runoff must be run within 21 days of the first elections. But diplomats in Harare and at the United Nations said Mr. Mugabe was planning to declare a 90-day delay to give security forces time to clamp down.

The questions about a potential runoff came a day after the senior leadership of the country’s ruling party decided that Mr. Mugabe should participate in a runoff with the opposition leader, if neither won a majority in last week’s election.

As if to highlight the continued resolve of ZANU-PF, the ruling party, the headline in Saturday’s online edition of The Herald, the state-run newspaper, read, “ZANU-PF readies for battle.”

Didymus Mutasa, the governing party’s secretary for administration, told journalists after an all-day party meeting that there was a consensus that Mr. Mugabe should run in a second round of voting.

“Mugabe, our dear old man, remains our candidate,” Mr. Mutasa was quoted as saying in The Herald. “We shall take him and carry him along with us.”

ZANU-PF officials also said they would seek a recount for 16 seats in Parliament’s lower house — enough to regain control if successfully challenged — alleging the opposition had bribed election officials and voters.

Still, a party leadership member, speaking on condition of anonymity because the deliberations were private, said the meeting was tense, with recriminations over the party’s weak showing in Parliament. Even before the election, he said, some members objected to Mr. Mugabe, 84, as the party’s standard-bearer, fearing that he would damage their own prospects of keeping their seats.

George Sitbotshiwe, a spokesman for the opposition, accused the electoral commission on Friday of being “in cahoots” with the ruling party, but said that even if it found that Mr. Tsvangirai had not won an outright victory, the opposition would still prevail in a runoff. “Even if he chops 1,000 heads off,” he will still lose the election, Mr. Sitbotshiwe said, referring to Mr. Mugabe.

In a crackdown on Thursday, the government staged raids against the Movement for Democratic Change, foreign journalists and at least one American democracy advocate helping local groups to monitor the election.

Mr. Mugabe, who has led Zimbabwe for all but a few months of its history, is widely judged a hero of the nation’s struggle against white rule. He has become deeply unpopular, though, as the economy has imploded and dissent has been stifled. Inflation has soared to a rate of 100,000 percent.

The streets were quiet in Harare, the capital, on Friday night after the meeting of the governing party’s leadership, the politburo. Few people were on the streets, except for riot police officers, who seemed to be in greater numbers in the city center than at any time since the recent troubles began. They walked in groups of four to eight, wearing blue helmets and carrying sticks.

People interviewed on the street said they were waiting for change in the country that they believed should have come by now. Nyasha Dube, a short, heavyset man in his late 20s standing near shops in downtown Harare, said, “People are holding on and they are feeling down.”

The A.P. reported earlier on Friday that hundreds of war veterans loyal to Mr. Mugabe had marched with a police escort through Harare to protest the opposition’s challenge to the government.

But one witness on the street described a much smaller, more subdued progression, perhaps no more than a few dozen: “There was no march, only the politburo members walking to the meeting alongside with war veterans, who are both supporters of Mugabe.”

Tsitsi, a woman in her 30s with long hair who gave only her first name for safety reasons, was leaving a take-out food shop in downtown Harare. She said many police officers on the street had cast hungry glances at the food she was carrying.

“The police are marching everywhere, up and down in the city center,” she said. “They are looking very hungry for food.”