President Obama and President Dmitri A. Medvedev of Russia in London back in April. Mr. Obama traveled to Russia on Sunday to conduct negotiations.

MOSCOW — Ahead of his departure for Moscow on Sunday night for a visit aimed at repairing strained relations with Russia, President Obama vowed not to sacrifice American support for greater freedom here and questioned the politically charged prosecution of a prominent Russian businessman.

Mr. Obama raised concerns about the treatment of the businessman, Mikhail B. Khodorkovsky, who along with his partner has been put back on trial six years after they were first arrested. Critics say the new trial seems aimed at keeping Mr. Khodorkovsky, an opponent to the government who was once Russia’s richest man, in prison.

“Without knowing the details, it does seem odd to me that these new charges, which appear to be a repackaging of the old charges, should be surfacing now, years after these two individuals have been in prison and as they become eligible for parole,” Mr. Obama said in written answers to questions posed by a Russian opposition newspaper, Novaya Gazeta, over the weekend. “Nonetheless, I think it is improper for outsiders to interfere in the legal processes of Russia.”

But Mr. Obama called on President Dmitri A. Medvedev to follow through on his promise “to strengthen the rule of law in Russia, which of course includes making sure that all those accused of crimes have the right to a fair trial and that the courts are not used for political purposes.”

In a television interview that was broadcast in Russia on Saturday night, Mr. Obama did not repeat critical comments that he had made about Vladimir V. Putin, the former president and current prime minister, who is widely considered Russia’s dominant leader.

Mr. Obama plans to conduct negotiations with Mr. Medvedev on Monday and have breakfast with Mr. Putin on Tuesday. In the interview on Russian state television, Mr. Obama was asked why it was important to meet both men. Mr. Obama noted that he had never met Mr. Putin, but added, “Obviously, he has been a very strong leader for the Russian people.”

The interview with Russian television was conducted on Thursday shortly after Mr. Obama offered a different view of Mr. Putin in an interview with The Associated Press.

In the A.P. interview, Mr. Obama said Mr. Putin had “one foot in the old ways of doing business and one foot in the new.” Mr. Obama said that it was time to move forward and that Mr. Medvedev “understands that.”

The comment was seen as provocative, and some American officials worried that Mr. Obama may have been too sharp in taking on Mr. Putin while others argued that it let the president come in a position of strength.

On Sunday, the Kremlin released the text of an interview in which Mr. Medvedev once again suggested that the United States needed to compromise on its proposed antimissile system in Eastern Europe in order to obtain a broader agreement on cutting nuclear arsenals.

Mr. Khodorkovsky’s case is one of three that have come up as Mr. Obama heads here. Supporters want him to press Russia not only to free Mr. Khodorkovsky but also to do more to pursue the killers of two journalists, Anna Politkovskaya, a crusading war correspondent, and Paul Klebnikov, an editor for Forbes magazine.

Ms. Politkovskaya held dual Russian and American citizenship while Mr. Klebnikov was an American of Russian heritage. Mr. Obama is sending top advisers to a memorial service to be held in Moscow on Tuesday for the fifth anniversary of Mr. Klebnikov’s death, and offered a show of support for Ms. Politkovskaya’s colleagues by answering written questions posed by her newspaper, Novaya Gazeta.

Novaya Gazeta’s editors, Dmitri Muratov and Andrey Lipsky, asked Mr. Obama if he would ratchet back American attention to liberty issues in Russia.

“Of course not,” Mr. Obama wrote, adding: “I agree with President Medvedev when he said that ‘freedom is better than the absence of freedom.’ So, I see no reason why we cannot aspire together to strengthen democracy, human rights, and the rule of law as part of our ‘reset.’ ”

Mr. Khodorkovsky, who led Yukos, Russia’s most successful oil company at the time, was arrested in 2003 when he challenged Mr. Putin. He was convicted of fraud and tax evasion and sentenced to eight years in prison, while his oil company was effectively taken over by the state. He is back on trial on new charges of embezzlement and money laundering.

Mr. Khodorkovsky’s parents hoped that Mr. Obama’s interest would prompt Mr. Medvedev to stop the trial and free their son. “I liked very much what Obama said,” his father, Boris Khodorkovsky, said in an interview. But Mr. Medvedev dismissed the possibility of a pardon, at least for now, comparing the case to the recent conviction of Bernard L. Madoff in the United States.

“Some businessmen have been given very long sentences, 150 years in the United States of America,” Mr. Medvedev said in his interview with Italian news media. “Why is it that somehow no one is unduly upset about this case?”