MOSCOW – Two deep-diving Russian mini-submarines descended more than 2« miles under North Pole ice to stake a flag on the ocean floor Thursday, part of a quest to bolster Russian claims to much of the Arctic’s oil-and-mineral wealth.

Despite the dangers of diving under 5-foot thick polar ice, both mini-submarines returned safely to the surface Thursday afternoon, the ITAR-Tass news agency reported, quoting Vice President of Federation of Polar Explorers, Vladimir Strugatsky.

The Mir-1 resurfaced after spending eight hours and 40 minutes under water and the Mir-2 mini-sub returned an hour later, Strugatsky said, according to Tass.

“It was so good down there,” expedition leader Artur Chilingarov, 68, a famed polar scientist said after coming back. “If someone else goes down there in 100 or 1,000 years, he will see our Russian flag.”

The voyage has some scientific goals, including studies of the climate, geology and biology of the polar region. But its chief aim appeared to be to advancing Russia’s political and economic influence by strengthening its legal claims to the Arctic.

Expedition organizers said the greatest risk facing the six crew members, three on each vessel, was being trapped under the ice and running out of air. Each sub had a 72-hour air supply.

Strugatsky said the Mir-1 had to spend about 40 minutes near the surface before it found a patch of sea free of ice, Tass said.

“That was difficult,” Chilingarov, who was aboard the Mir-1 three-person sub, told a cheering colleagues, who welcomed the crew with loud “hurrah!” after the mini-sub was raised to the Akademik Fyodorov research ship.

The crew of the Mir-1 dropped a titanium capsule containing the nation’s flag on the bottom, symbolically claiming almost half of the planet’s northern polar region for Moscow.

The Mir-2’s crew included Michael McDowell, an Australian described by the ITAR-Tass news agency as a polar explorer, and Frederik Paulsen, a Swedish pharmaceuticals millionaire described as a co-sponsor of the dive.

Russian scientists planned to map part of the Lomonosov ridge, a 1,240-mile underwater mountain range that crosses the polar region. The ridge was discovered by the Soviets in 1948 and named after a famed 18th-century Russian scientist, Mikhail Lomonosov.

In December 2001, Moscow claimed that the ridge was an extension of the Eurasian continent, and therefore part of Russia’s continental shelf under international law. The U.N. rejected Moscow’s application, citing lack of evidence, but Russia is set to resubmit it in 2009.

If recognized, the claim would give Russia control of more than 460,000 square miles – almost half of the Arctic seabed. Little is known about the ocean floor near the pole, but by some estimates it could contain vast oil and gas deposits.

Before Thursday’s dives, researchers mapped the location of natural openings in the polar ice. The icebreaker Rossiya spent most of Wednesday night and Thursday morning carving a 400×30 foot artificial opening near the pole, RTR television reported.

Gruzdev joked about what the submarines might find, Russia’s Channel One reported.

“And what if we encounter Atlantis there?” Gruzdev said. “Nobody knows what is there. We must use the opportunity given to us 100 percent.”

The deepest dive on record, according to several sources, was by the bathyscaphe Trieste, which in January 1960 descended 35,810 feet into the Mariana Trench in the Pacific.

In the coming weeks, expedition researchers plan to set up an Arctic research camp near the pole, called a “drift station” because it will drift with the shifting ice pack in the polar sea, to carry out long-range climate studies. The scientific research ship Akademik Fyodorov is expected to remain in the region until mid-September.

U.S. State Department spokeswoman Leslie Phillips said, “We wish the Russian scientists a safe expedition.”

The U.S. Senate has not yet ratified U.S. accession to the U.N. Law of the Sea, which would give Washington a seat on the panel that will consider and eventually rule on the Russian Arctic seabed claim.

Phillips said the Bush administration would continue to press hard for ratification in order to give the United States a voice on that commission.