A newcomer to Russian politics, the billionaire owner of the New Jersey Nets, jumped into the race for president Monday in a challenge to Vladimir Putin that would have been laughed off as quixotic just two weeks ago.

But the announcement by Mikhail Prokhorov caused a stir instead. The political landscape in Russia appears to have shifted so dramatically after a week of protests over alleged fraud in parliamentary elections this month that a path may now exist for an oligarch preaching economic development who wants to take on the country’s strongman.

Prokhorov brings a considerable fortune to his task, as well as a reasonably high profile. At 46, he presents a modern outlook and would seem to be on the same wavelength as many of the middle-class Russians who have become disenchanted with Putin and are calling for his defeat in the March presidential election.

First, though, Prokhorov will have to prove himself. The tens of thousands of protesters who have come out on the streets of Russia in the past week are supporting a cause, not following a leader.

That cause is promoting clean elections and, beyond that, a clean and representative government. The most direct way to achieve those results would be to beat Putin in the upcoming election — but that’s still not likely. Prokhorov’s announcement notwithstanding, no single man or woman has emerged as the obvious challenger.

The opposition forces — which embrace everyone from nationalists flying the czarist flag to communists with the hammer and sickle to liberals intent on individual rights — are deeply riven, even now. They are bound only by their desire to get rid of the system that Putin erected.

New faces, many from a younger generation than the current crop of politicians, are gaining prominence. The jailed blogger Alexei Navalny, 35, has become a hero to his readers. But neither he nor Prokhorov — nor anyone else — has demonstrated the authority or character to unite the broad array of protesters and steer the movement to victory.

Some here argue that three months is time enough to sort out a campaign against Putin. Others say the protesters are really looking beyond March, conceding that Putin is the likely winner but hoping to lay the groundwork for deeper change later on.

Where Russia goes from here, and how, is a question being asked in Washington, too. The Senate Foreign Relations Committee has scheduled a hearing Wednesday on the state of human rights and rule of law in Russia. The parliamentary elections and the subsequent protests are sure to be part of the testimony.

Legitimacy questioned

On Monday, Prokhorov said he plans to campaign on a platform of economic development, which would entail weaning Russia off its financial dependence on oil revenue and strengthening the middle class.

Prokhorov’s appearance coincided with the publication of an interview with Alexei Kudrin, Putin’s well-regarded former finance minister, in the newspaper Vedomosti. Kudrin advocated a sensible liberal opposition to Putin’s United Russia party, which could dovetail with Prokhorov’s plans. Kudrin had a falling out with Putin in September, when he left the government.

Prokhorov’s decision to challenge Putin comes eight years after another Russian billionaire, Mikhail Khodorkovsky, was hauled off to jail. Khodorkovsky was just thinking about getting into politics when he was arrested. Prokhorov said Monday that he is not worried about meeting the same fate.

Prokhorov, who became the first overseas NBA owner when he bought the troubled Nets franchise last year, had a strange and sour try at politics earlier this year. Many of his potential allies considered him a Kremlin puppet; some still do. And he has a penchant for striking odd notes.

“I will build my manifesto on the total absence of populism. I will be saying only what I consider necessary,” he said Monday at a news conference. “I am perfectly aware that some ideas are certain not to win a majority, but I think it is my civic duty to deliver information about what is going on in the world.”

Putin’s political aides have long suggested that United Russia needs a tame liberal opposition. They persuaded Prokhorov to try to build one in June but turned against him in September. Prokhorov denounced the Kremlin, but his legitimacy as an opposition leader is still questioned.

Boris Nemtsov, a deputy prime minister in the 1990s and a politician who strikes many voters as a throwback to a long-gone and unlamented era, immediately slammed Prokhorov. The criticism matters because Nemtsov’s political movement, Solidarity, is one of the chief sponsors of the protests.

Nemtsov said Prokhorov and Putin were in cahoots, playing “an obscene game,” according to the Interfax news agency.

“It is absolutely impossible to imagine that that billionaire didn’t have the go-ahead from Putin for putting himself forward as a candidate for the presidential election,” Nemtsov said.

That was nastier than anything Putin’s backers were saying Monday. United Russia staged a rally in Manezh Square, bringing in a few thousand young supporters by bus from as far away as Kaluga and Bryansk. The mood was festive and friendly, which was a change from the hostility that prevailed at a similar rally last Tuesday.

“We work with drug addicts, and we really need the support of the authorities,” said Marina Sadovskaya, 27, who volunteers at a drug rehabilitation center. “Now the authorities need our support.”

It was good to see so many young people backing United Russia, she said. But, she added, it was sad that they had come only because their schools and clubs had arranged to bus them in: “We just wish they’d do it of their own free will.”

Few options in opposition

The Communist Party finished a strong second in the elections, and its backers have suggested that the opposition rally around its leader, Gennady Zyuganov, in the presidential race.

The Communists have the advantage of a strong and thorough network throughout the country. Their disadvantage is Zyuganov, a former Soviet apparatchik who is notably colorless. Zyuganov — like the flamboyant Vladimir Zhirinovsky, head of the nationalist Liberal Democratic Party — shows every sign of having accepted his role as leader of a permanent but comfortable minority. Putin allows them to take part in politics, as long as they don’t cause any trouble.

Navalny, the crusading anti-corruption blogger, declined to become a candidate earlier this year. At the moment, he is serving a 15-day sentence after getting arrested on the first day of post-election protests. His arrest made him a hero to millions. When he gets out, he will be at the forefront of the opposition, but he may be more effective, as he himself has suggested, staying out of politics.

Prokhorov, meanwhile, could draw support from Russians who are well off and haven’t traditionally paid much attention to politics but are seething at the corruption and arrogance in government, suggested Matthew Rojansky of the Carnegie Endowment for International Peace in Washington.

“Prokhorov, simply put, is a creature of 2000’s Russia — of the Putin era,” Rojansky wrote in an e-mail. “He may thus be the best equipped to lead a campaign to bring it to an end.”