Two Russias faced off in Moscow on Tuesday night — the blogging social media generation, risen up from their laptops in protest against Sunday’s elections and the status quo, and busloads of students brought in from small towns to demonstrate their support for the ruling United Russia party and preserve the status quo.

Police arrested a steady stream of the opposition protesters at Triumfalnaya square, reportedly 300 in all, among them veteran human rights activists and longtime opposition politicians from an older generation. The pro-Kremlin youths provided a soundtrack — banging drums and shouting, “Russia, Russia, Russia” — as police dragged the detainees away.

At a courthouse nearby, a judge was sending the country’s most prominent blogger to jail for 15 days for his role in a demonstration the night before against election fraud and Prime Minister Vladimir Putin. Alexei Navalny, the crusading anti-corruption activist, had helped galvanize 5,000 demonstrators, the largest opposition rally in many years.

By packing him off to jail, on a charge of disobeying police, the government may have elevated him to new heights of stardom in the eyes of his Web followers — and to new visibility for everyone else in the country.

Russia’s leaders have been accused of making many mistakes in the past weeks. This one, said Alexei Venediktov, editor in chief of the relatively independent radio station Echo Moskvy, was their worst.

The opposition has many earnest leaders, but none who unites and inspires the new Russia standing on one side of the square Tuesday. Now the government may have given them one: Navalny, a 35-year-old self-described “nationalist democrat.”

The opposition, characterized more than anything by a lack of agreement among its members, is made up of longtime human rights activists, liberal politicians mostly shut out of the political process and an array of activists associated with causes, such as the environment and the rights of automobile owners. Philosophically, the disaffected middle class drifts toward them, but they are not allied in one strong political movement.

With its once-deep support falling away because of a poor economy and an atmosphere of stagnation, United Russia has come to rely on those dependent on the government for jobs or access.

Those shouting for Russia in the square, although young, were part of the old Russia represented by United Russia, from youth groups carefully nurtured by the Kremlin or those dependent on local authorities. Most refused to talk, saying they were not allowed to say a word. “We were brought from Samara,” said one young man, describing a 450-mile trip that took 15 hours. “We didn’t expect this. I hope they’ll let us go soon.”

Navalny famously dubbed United Russia as the “party of crooks and thieves,” a name that stuck so firmly that even the Communist Party throws about the term. Though he is well known, he has not strayed into politics. Now supportive messages for him flow like a waterfall on Twitter.

‘They are nobody’

Putin said Tuesday that a falloff in support was to be expected, given the strains that Russia has been experiencing. He dismissed the accusation that United Russia was in any way uniquely corrupt. He promised to shake up the government after he becomes president in March, as expected.

But bribery and extortion here are thought to have mushroomed under Putin, and Navalny’s attacks on the system have made him a hero. His stands against corruption and authoritarianism, and in defense of ethnic Russians, tap a deeply popular root here among people who are mistrustful of the Western-oriented liberal old guard.

“This is our enemy, and we hate him!” he told the crowd of several thousand demonstrators Monday night. “We should remember that they are nobody. And we are the power. We do not need thieves and crooks! We want another president and not a thief and crook!”

The crowd began chanting, “Putin is a thief!”

Shortly after, Navalny and about 300 others were detained. Most were soon released.

On Tuesday, pro-Kremlin youth groups had promised that thousands upon thousands would fill Moscow in support of United Russia, Putin and President Dmitry Medvedev. The numbers fell far short. Only several hundred young people gathered for a concert, outnumbered by rings of police, near the Kremlin and Revolution Square. Mostly, police officers stared impassively, a few smoking, others harshly pushing along reporters who blocked the sidewalk. And they were rough with those they detained.

A 20-year-old student named Natasha, who came from near Smolensk 230 miles away, said the buses had been organized by the local administration, and students were told to get on them. “Shhhhh,” her friend told her. “We’re not supposed to say that.”

‘Absolute discrimination’

At Triumfalnaya square, a 27-year-old named Denis said he had voted for a liberal party and wanted to ask the pro-Kremlin demonstrators about their views. None would talk to him.

As Denis was talking, Boris Nemtsov, a political leader of the 1990s and now a Putin opponent, was arrested as he approached the square, just yards from where he was detained on New Year’s Eve in a rally in support of the freedom of assembly guaranteed by the constitution. In December, he got 15 days. On Tuesday, he was soon freed.

At one point, the Associated Press reported, two firecrackers were thrown into the crowd, but it was not clear by whom.

Some knots of the opposition, perhaps unrecognized by police, started to gather without hindrance, but when they identified themselves by shouting “Putin’s a thief,” they were arrested, too.

“What I saw was an absolute discrimination,” Oleg Orlov, head of the Memorial human rights association, told the Interfax news agency. “At the center of the square were youth activists standing under police protection, beating drums and chanting slogans. All others who were shouting something else are being taken and dragged and beaten.

Eventually, everyone went home Tuesday. About two dozen pro-Kremlin youths were spotted in the subway, lined up two-by-two, as if returning home from a school field trip. Many of the detained were slowly being released.

And no one knew whether the young generation had taken a breath of fresh air and returned to their laptops, or whether something had changed forever.