MOSCOW — Dmitry Medvedev, the man President Putin hand-picked to be his successor, scored a crushing victory in Russia’s presidential elections today, a result that was long anticipated but that raises questions about who will run this resurgent global power.

With ballots from two-thirds of the polling stations counted, Mr. Medvedev had 69% of the vote, according to the Central Election Commission. The Communist Party chief, Gennady Zyuganov, had 18%, it said.

Mr. Medvedev was on course to win about 70%, according to a poll by the All-Russia Opinion Research Center, or VTsIOM.

He is expected to rule in concert with his mentor, an arrangement that could see Mr. Putin calling the shots despite his constitutionally subordinate position as Russia’s prime minister.

Mr. Medvedev, 42, the youngest Russian ruler since the 1917 Bolshevik Revolution, is expected to heed Mr. Putin’s advice, continue his assertive course with the West, maintain state control over Russia’s mineral riches, and freeze out real opposition movements.

“We will increase stability, improve the quality of life and move forward on the path we have chosen,” Mr. Medvedev said today, appearing alongside Mr. Putin at a celebration at the Red Square outside the Kremlin. “We will be able to preserve the course of President Putin.”

Mr. Putin said Mr. Medvedev “has taken a firm lead” and congratulated his protege.

“Such a victory carries a lot of obligations,” Mr. Putin said. “This victory will serve as a guarantee that the course we have chosen, the successful course we have been following over the past eight years, will be continued.”

Mr. Medvedev ran against three rivals apparently permitted on the ballot because of their loyalty to the Kremlin line. But the two candidates — Mr. Zyuganov and ultranationalist Vladimir Zhirinovsky — still alleged violations after the voting ended.

Mr. Zyuganov said he would dispute the result, and Mr. Zhirinovsky threatened to do so as well, before backing down.

Some voters complained of pressure to cast ballots for Mr. Medvedev, and critics called the election a cynical stage show to ensure unbroken rule by Mr. Putin and his allies.

Today’s vote came after a tightly controlled campaign and months of political maneuvering by Mr. Putin, who appeared determined to keep a strong hand on Russia’s reins while maintaining the basic trappings of electoral democracy and leaving the constitution intact.

Mr. Medvedev has said he would propose making Mr. Putin his prime minister, and Mr. Putin has said he would agree. But in Russia, the premier wields significantly less power than the president, and Mr. Putin may find his new chair narrow and confining.

At a news conference, Mr. Medvedev was asked who would run foreign affairs — him or the prime minister. “Under the constitution, the president determines foreign policy,” he said.

After eight years in the international limelight, Mr. Putin may miss the job of representing Russia in gatherings of world leaders.

The first test could be the July summit of Group of Eight leading industrialized nations: If Mr. Putin goes alone or accompanies Mr. Medvedev, that could signal his reluctance to relinquish control.

Russia had two rulers — a diarchy — in the 17th century, when the first Romanov czar, Mikhail, served along with his father, Patriarch Filaret. In the early 1920s, Josef Stalin briefly shared power with the Bolshevik leader and founder of the Soviet state, Vladimir Lenin.

The Putin-Medvedev tandem could encourage a revival of classic Kremlinology. During the Soviet era, Western experts painstakingly studied power shifts in the Kremlin by noting minute details of the public appearances of Communist Party leaders.

In particular, they looked for signs of tension or bad blood in body language, and of rising or falling influence based on where they stood on Lenin’s Tomb during annual parades in Red Square.

Mr. Putin already has shown signs of discomfort with his new role as subordinate to his protege.

When a reporter at his last news conference in February asked him whether he would put the new president’s portrait on his office wall, Mr. Putin answered dryly that he doesn’t need to make such displays of loyalty.

Some officials who know Mr. Medvedev say privately that he is tougher than his appearance and demeanor may suggest and could show more resolve after his inauguration.

Mr. Medvedev has taken a liberal and pro-business posture during the campaign, avoiding Mr. Putin’s harsh anti-Western rhetoric. But critics point that he helped engineer Mr. Putin’s crackdown on political and media freedoms as one-time Kremlin chief of staff.

He also spearheaded the Kremlin’s concept of making Russia an “energy superpower” as chairman of Gazprom state gas monopoly, strong-arming former Soviet neighbors and expanding Russia’s control of Europe’s energy supplies. Mr. Medvedev’s landslide victory would give him the stature to defy Mr. Putin, in case of any potential rift with his mentor.

While most expect Mr. Medvedev to play second fiddle to Mr. Putin, the vast powers of the Russian presidency may tempt him to step out of his mentor’s shadow.

Russian history shows that rulers often like to get rid of those who backed their ascent to power. Boris Berezovsky, who backed Mr. Putin’s rise to power, fled abroad to escape money-laundering charges several months after his election.

Mr. Medvedev is the first Russian leader to succeed his predecessor according to a constitutional timetable; Mr. Putin became acting president first after Russia’s first President Boris Yeltsin stepped down early, and only later won election.

But Mr. Medvedev’s election was not a wide-open contest either.

Liberal opposition leaders, Garry Kasparov and Mikhail Kasyanov, were barred from running on technicalities, and voters across Russia say they were being urged, cajoled, and pressured to vote in an effort to ensure that Mr. Medvedev scored a major victory.