MOSCOW — President  Dmitri A. Medvedev’s state of the nation address went on for 85 minutes and contained more than 8,000 words, but the section that prompted the most chatter on Thursday was a single sentence, the one that proposed lengthening the Russian president’s term to six years from four.

The proposal in the televised speech on Wednesday sounded odd, coming from a man just four months into his first term, and he offered little insight into his motive. It has led to rumors that Mr. Medvedev was laying the groundwork for his mentor,  Vladimir V. Putin, the former two-term president who is now prime minister, to return as president, perhaps as early as next year.

Thursday’s issue of Vedomosti, a respected financial daily newspaper, fleshed out this theory in all its conspiratorial glory. Citing an unnamed source close to the presidential administration, Vedomosti reported that Mr. Putin intentionally placed Mr. Medvedev in the presidency “to carry out the necessary constitutional changes and unpopular reforms for Putin to then return to the Kremlin for longer.” The newspaper theorized that Mr. Medvedev would resign and call for a presidential election in 2009.

Dmitri Peskov, a spokesman for Mr. Putin, called the report “nothing more than the speculation of a newspaper.”

“Mr. Medvedev is in the initial stage of his presidency,” he said. “Now is not the time to think about the next presidency in  Russia. We still have a long time to go and lots of things to do.”

Asked whether Mr. Putin intended to run for a third term, he said, “Consider a question to anyone in Washington whether Mr. Obama will run for another term.” Russian presidents are allowed to serve no more than two consecutive terms.

In his speech on Wednesday, Mr. Medvedev said he would like to amend the Constitution to lengthen the presidential term to six years and the term of Duma deputies to five years. He noted that such changes had been discussed by leaders in Moscow since the 1990s.

Kremlin officials said later in the day that the change would not apply to incumbents.

A bill will likely be submitted to the State Duma, the lower house of Parliament, within the next two weeks, Boris Gryzlov, the body’s chairman, told the Interfax news agency on Thursday. To pass, it must be approved by two-thirds of the State Duma, three-quarters of the Federation Council and two-thirds of Russia’s local assemblies.

The proposal provoked a tumult of commentary.

“It’s clear to me that the change was done for the benefit of clan, or class, or group interests, and against the interests of Russia, because what Russia needs is change,” wrote Dmitri Oreshkin, a political scientist, on the Web site Grani.ru. “We have become involved in the process of global change, and if we lag behind, we will turn into a stagnant backwater. Not even a backwater — a wildlife sanctuary.”

Alexander Rahr, a Russia expert at the German  Council on Foreign Relations, said the notion of Mr. Putin’s return had been discussed openly, with some theorizing that Mr. Putin had wanted to stay on without amending the Constitution himself. If Mr. Medvedev makes the change, “it is more clean, because it’s another president proposing this, not himself,” Mr. Rahr said.