Mr. Medvedev’s importance in the government has seemed to recede as the country prepares for Mr. Putin to return to the presidency. During his question-and-answer session on Thursday that lasted more than four hours, Mr. Putin mentioned Mr. Medvedev only once. Kremlinologists took this as evidence that Mr. Medvedev can no longer expect to be appointed prime minister in the spring, as Mr. Putin had promised. Even if that is the case, Mr. Medvedev will retain extraordinary constitutional powers and access to the media for as long as he remains president.

“We are obviously entering a new stage in the development of our political system, and we should not close our eyes to that,” Mr. Medvedev told members of United Russia, according to an official transcript. “It has already begun. And it began not as a result of some demonstrations — that is just superficial, it is foam, if you like — it is a manifestation of human dissatisfaction.

“It began because the old model — which faithfully and truly served our state in recent years, and didn’t serve it badly, and which we all defended — it has exhausted itself,” Mr. Medvedev said, adding that United Russia should take a leading role in proposing reforms. “We need to change the model, and only then will there be dynamic development in our country.” He warned that Russia will face disaster if the public ceases to view the government as genuinely elected — a danger, since Mr. Putin is likely to run against a slate of docile, Kremlin-approved candidates, on the heels of the parliamentary elections that have drawn anger.

“It is categorically inadmissible that the political system be delegitimized,” Mr. Medvedev said. “This would only mean one thing for our country: the collapse of the state. What Russia is without government is something that everyone remembers well from history books, it’s 1917.”

The Russian authorities have said that American leaders were interfering by publicly criticizing the elections, and Mr. Medvedev said he had raised complaints with President Obama in a telephone conversation on Friday.