Western observers reported Monday that the results of Russia’s parliamentary elections were seriously distorted by ballot stuffing and a lack of transparency, which suggests that the ruling United Russia party did even worse than the official count showed.

The international monitors said the election process was slanted in favor of United Russia throughout the campaign and compromised by the use of state resources on the party’s behalf. They especially criticized what they called partiality by the election commission.

The widespread conviction that the results were inflated on behalf of United Russia set off a demonstration larger than any Moscow has seen in years, with 5,000 or more youthful protesters gathering around Chistye Prudy boulevard before police dispersed them Monday evening. Opposition demonstrations normally attract only a few hundred protesters, as did one in favor of fair elections the weekend before the vote.

Secretary of State Hillary Rodham Clinton, speaking in Bonn, Germany, said the United States had “serious concerns” about the conduct of the vote, adding: “Russian voters deserve a full investigation of all credible reports of electoral fraud and ma­nipu­la­tion.”

Despite all its advantages, Prime Minister Vladimir Putin’s party won slightly less than half the ballots cast Sunday, according to near-final results announced Monday. That will ensure United Russia’s continuing control of the state Duma but, for the first time, raises the possibility that Putin’s formidable political machine may have its vulnerabilities.

Politicians and political scientists agree that Putin’s election as president March 4 has not been jeopardized — he has always been more popular than United Russia and has managed to keep the opposition in disarray during two terms as president and the past four years as prime minister. One especially disliked party was not allowed to run in the elections. Another was destroyed after its leader became too independent.

But there is also widespread agreement that the voters have sent a loud, though ambiguous, message. It came mainly from the new middle class and city dwellers, who were demanding change without explicitly endorsing a specific direction. No strong opposition emerged to rally them, and many gravitated toward the familiar and always well-organized Communists.

“This new political stratum wants change,” said Sergei Markov, a Duma deputy and United Russia member, “but they didn’t decide what kind they want. They have no political champions.”

Putin and United Russia must change to get them back, he said, reviving the economy and raising the pay of teachers, doctors and engineers. The moral climate also must be improved, Markov said. “There shouldn’t be this feeling that Russia belongs to those stealing money, not those who are working,” he said.

Boris Makarenko, deputy director of the Center for Political Technologies, said United Russia’s first loss of Duma seats would force the party to change.

“They are accustomed to a supermajority where no one could even think of challenging them,” he said, and they will have to learn how to respond to criticism, compromise and sell their ideas to the public.

Markov was philosophical about United Russia’s drop from 64.3 percent of the vote in the previous parliamentary elections, four years ago, to 49.35 percent. “That was huge,” he said of the 2007 vote. “It was too much.”

The Communists were the biggest beneficiaries, getting 19.18 percent of the vote; Fair Russia, a self-described social democratic party created in 2006 with the Kremlin’s blessing, won 13.24 percent; the nationalist Liberal Democratic Party took 11.67 percent; and liberal Yabloko got 3.41 percent.

The troubled Caucasus was one region unswerving in its support. Turnout in Chechnya was reported at 99.51 percent, with United Russia at 99.47 percent. Dagestan, where violence and terrorism has taken root after the pacification of Chechnya, gave United Russia nearly 92 percent of the vote, as it did in 2007.

“Ninety-two percent is terrific and terrible at the same time,” said Sergei Markedonov, a scholar at the Center for Strategic and International Studies in Washington. “In the Caucasus, it is necessary to prove your loyalty to the Kremlin, so there will be no interference.”

In Russia, Putin’s party has become synonymous with the government. Although election monitors pointed that out as a fault, the prime minister finds it a source of pride.

“United Russia is a party the government has relied upon in the past years. It would not be an exaggeration to say that United Russia has been a major cornerstone of our strategic stability,” Putin said Monday.

Grigory Melkonyants, deputy director of Golos, Russia’s only independent election monitor, said numerous election violations were observed, but especially the interference by the administration.

“Many voters who work for government agencies or depend on representatives of power in one way or another were forced to vote a certain way,” he said. “We have many doubts about the results.”

Observers from the Organization for Cooperation and Security in Europe monitored the vote count at 115 polling places and found evidence of ballot stuffing at 17.

“It’s a major insult to all those who voted,” said Tiny Kox, head of one of the OSCE’s delegations.

Russia, said Petros Efthymiou, another OSCE leader, “did not provide the necessary conditions for free and fair elections.”

The observers refrained from denouncing the elections categorically. Efthymiou said they had not come as prosecutors, and Kox pointed out that though flawed, the result signals a significant change in Russian politics.

“Not everything was fixed,” he said, “and the vote really matters.”