MOSCOW — President Obama and Russian President Dmitry Medvedev struck a preliminary deal today to reduce their nations’ stockpiles of nuclear warheads to as few as 1,500 each, pointing their arsenals toward the lowest levels of any U.S.-Russia arms control agreement.

The document signed by the two leaders at a Moscow summit, Obama’s first in Russia, is meant as a guide for negotiators as the nations work toward a replacement pact for the START arms control agreement that expires in December. The joint understanding completed by Obama and Medvedev, signed after about three hours of talks at the Kremlin, also commits the new treaty to lower longer-range missiles for delivering nuclear bombs to between 500 and 1,100.

Under current treaties, each country is allowed a maximum of 2,200 warheads and 1,600 launch vehicles.

A White House statement said the new treaty “will include effective verification measures.”

“The new agreement will enhance the security of both the U.S. and Russia, as well as provide predictability and stability in strategic offensive forces,” the statement said. The two leaders were to appear together at a Kremlin news conference to discuss their agreement.

The leaders announced several other deals meant to show progress toward resetting badly damaged U.S.-Russian relations, including permission from Moscow for the United States to transport arms across its land and airspace into Afghanistan for the war there. The White House says the deal will save the U.S. $133 million a year, by waiving transit fees and shortening flying time.

They outlined other areas in which they said their countries would work together to help stabilize Afghanistan, including increasing assistance to the Afghan army and police, and training counternarcotics personnel. A joint statement said that they welcomed increased international support for upcoming Afghan elections and that they were prepared to help Afghanistan and Pakistan work together against the “common threats of terrorism, extremism and drug trafficking.”

Other side agreements meant to sweeten Obama’s two days of talks here include revival of a joint commission to try to account for missing service members of both countries dating back to World War II and fresh cooperation on public health issues.

Obama needs Russia’s help chiefly in pressuring Iran and North Korea to give up their nuclear weapons ambitions, but also in tackling terrorism, global warming and the economy. But with Russia’s public wary of America and relations frayed with Moscow’s war with Georgia last year and U.S. missile defense plans in Eastern Europe, his desire to reboot relations is a huge test of his diplomatic skills.

“The United States and Russia have more in common than they have differences,” Obama said earlier as he and Medvedev first sat down in an ornate Kremlin room.

His host launched the high-stakes summit with similar good will.

“We’ll have a full-fledged discussion of our relations between our two countries, closing some of the pages of the past and opening some of the pages of the future,” Medvedev said, through a translator.

Yet, the two sides remain stalemated over the U.S. pursuit of a missile-defense system in Europe, pushed hard by Bush and under review by Obama. Both sides hardened their positions ahead of the summit.

The U.S. contends the program is designed to protect U.S. allies in Europe from a potential nuclear attack by Iran. But the Russians see it as a first step toward a system that could weaken their offensive nuclear strike potential.

The summit starts a weeklong trip for Obama that also features G-8 meetings and a visit with the pope in Italy, and a speech in Ghana.

After Obama landed in Moscow under drizzly gray skies, he introduced his wife, Michelle, and their two daughters to the Russian officials waiting to greet them on the tarmac. The entourage then headed to a wreath-laying ceremony at Russia’s Tomb of the Unknown Soldier.

Having enjoyed adoring crowds in other parts of Europe, Obama will face a far more skeptical Russian population.

Just 15 percent of Russians say the U.S. is playing a positive role in the world; most said the United States abuses it power and makes Russia do what the U.S. wants, according to the University of Maryland’s WorldPublicOpinion.org out Sunday.

“I would like to see America meddle less in other countries,” said Valentina Titova, a 60-year-old retired economist strolling not far from the Kremlin.

Obama will outline his vision for U.S.-Russian relations at a speech at the New Economic School. It is unclear how many people will see it. Russian leaders control the television outlets.

As Obama told a Russian-language news channel in the days before the summit: “We want to build relations where we deal as equals.”

Yet he also caused a stir in Russia by telling The Associated Press last week that Medvedev’s predecessor and mentor, Prime Minister Vladimir Putin, has to learn that “the old Cold War approaches to U.S.-Russian relations is outdated.”