MOSCOW — The Russian authorities acted decisively to quash a second day of protests against the government and Prime Minister Vladimir V. Putin on Tuesday, flooding the appointed site with throngs of pro-government activists who banged on tin drums, drowning out the chants of “Russia without Putin!”

Several hundred protesters convened in a central square, hoping to maintain the momentum from Monday, when as many as 5,000 protested alleged fraud in parliamentary elections. The smaller crowd that formed Tuesday, however, was rapidly choked off by riot police officers who dragged many of them away.

Police officials told the Interfax news service that 250 people had been detained, slightly fewer than the 300 who were detained Monday. Even as those reports filtered out, antigovernment activists were calling via Twitter for a third round of protests on Wednesday.

The authorities have made an example of two of the leaders of Monday’s protest — a liberal activist, Ilya Yashin, and the blogger Aleksei Navalny, who famously branded Mr. Putin’s party, United Russia, “the Party of Swindlers and Thieves.” Both men were sentenced to 15 days in prison on Tuesday for disobeying police orders. Supporters camped out on the street in hopes of glimpsing Mr. Navalny, sharing cold cuts and thermoses of tea and a mood that was almost giddy because of Monday’s turnout.