BAKU, Azerbaijan, Nov. 6 -After months of pre-election tension in a nation that has never had a free and fair election under its ruling family, voters in Azerbaijan cast their ballots for Parliament on Sunday amid new accusations of fraud and government abuses.

The turnout appeared modest, with the preliminary government figures from many districts showing 40 percent to 50 percent of eligible voters casting ballots and the ruling party with a firm official lead in seats for the 125-member Parliament. The day was largely peaceful, if chaotic.

But the possibility of violence remained, as the government and its opponents came to starkly different conclusions about the conduct of the vote and ballot counting and as the government appeared to have tampered with the results of at least one prominent race.

The ruling Yeni Azerbaijan Party declared victory even as the count continued, while leaders of Azadliq, a three-party opposition bloc, said the official results were a sham and races were tainted by falsification, fraud and police action. Ali Kerimli, leader of the Popular Front of Azerbaijan Party, a bloc member whose evident leads in several polling places were rejected by the authorities, called for demonstrations on Tuesday.

Unauthorized opposition demonstrations in the past have been dispersed with force, and the riot police - with helmets, shields and batons - were posted outside the Government House on Sunday night. The government has made clear that unapproved rallies will be broken up.

What is at stake in the election is the international reputation of Azerbaijan, a small, oil-rich nation on the Caspian Sea that has built close ties with the United States, as well as that of its young president, Ilham Aliyev, 43.

Mr. Aliyev was the political heir of his father, Heydar Aliyev, who ruled the country through most of its independence. The younger Mr. Aliyev came to power in October 2003 in an election marred by fraud and followed by violence. His father died in December of that year.

Since then, as elections in the post-Soviet sphere have received greater scrutiny and attention after revolutions in Georgia, Ukraine and Kyrgyzstan, Mr. Aliev has promised to hold fair elections.

This year he promised candidates more access to television campaigning and greater freedom of assembly. He also pledged to curb the abuse of government resources in support of pro-government candidates.

He agreed to allow international pollsters to survey voters leaving voting places, and, after international monitors complained in October that the potential for fraud remained, to allow indelible ink kits to be used for marking voters' thumbs to prevent multiple voting.

Mazahir Panahov, chief of the central election commission, predicted Saturday that the conduct of the election would be proper.

But the opposition and international organizations have said the pledges were undermined by the government's behavior during the campaign, including beatings of demonstrators, arrests of opposition figures and continued use of government resources for its candidates.

"What we have is a criminal authoritarian regime, and they do not even think of the possibility of passing power to the people," said Isa Gambar, leader of the Musavat Party, another bloc member.

Hours after voting started Sunday morning, reports of abuses began streaming in, including claims of vote-stuffing, vote-buying, multiple voting at polling places where ink was not used or not checked, and the presence of party officials or observers who were telling voters who should get their vote. Suspicious activities or irregularities were readily observable.

At School No. 246 here in the capital, men clustered around the polling place, warily watching voters come and go. During an interview with a voter, one of the men strolled over to listen, and the voter - who a moment before said she did not think the election was democratic - said, "I am for Aliyev."

At another polling place, in the district where Mr. Gambar is running, a large man stood in the hall. Four election observers said he was telling voters to vote for "No. 3," a senior police official. The man in the hall, Surhan Mamedov, 36, said he was simply greeting people.

The observers said another man had been seen giving 50,000 manat, about $10, to a voter in exchange for voting for the police official. Mr. Mamedov said that was untrue.

In Zyra, where the president's wife was running, one woman left a voting booth holding three ballot envelopes, heading for the ballot box. As a correspondent took her photograph, the head of the local electoral commission, Dilshot Askerova, rushed over and led her back behind the curtain.

The two women spoke heatedly but quietly, then the voter returned with a single vote and placed it in the transparent box. She refused to be interviewed, and appeared frightened.

The two ballot boxes at that polling place also appeared to have been stuffed by people casting multiple simultaneous votes, as many ballot envelopes inside had been folded together and were resting in creased packets of four to eight votes.

Whether these irregularities influenced the outcome was not immediately clear. Officials from international observer missions said it was too soon to put the reports of abuses into a full context. An official monitoring report by the Organization for Security and Cooperation in Europe was expected Monday, after winners were declared.

The government's heavy-handed behavior continued into the night, however. Officials at the district where Mr. Kerimli is running refused to accept counts that put him ahead in several polling places, multiple witnesses said. The police were called and observers ordered away, the witnesses said.

The police could be seen ringing the district headquarters, where tallies were being recounted without any independent or opposition observers. One woman said she had seen new ballots dumped in with the old as the police came in and before she was ordered to leave.

"This is an open violation of democratic standards and norms," said Murad Gassanly, one of Mr. Kerimli's advisers.

Elin Suleymanov, an adviser to the president's office, said he had heard of what he called isolated abuses. He said that such things were unavoidable in a young nation like Azerbaijan, which gained its independence after the breakup of the Soviet union in 1991, and that they were not necessarily very significant.

"It is inevitable that certain friction and certain tension will appear," he said. "Democracy in general takes a certain effort to develop." He added that in his view, Azerbaijan was holding the cleanest and freest election in its history.

Viktor Klimenko contributed reporting for this article.