Russia is reportedly sea testing a nuclear-powered sub believed superior in many ways to some of America's best subs.

The Gepard (Russian for cheetah) it is expected to begin active duty with the Northern Fleet as early as July, after it passes its trials, according to Russian news reports.

U.S. sub experts suspect the Gepard may move as fast and as quietly as America's best fully operational subs, the Los Angeles-class subs, as well as have the capacity to dive deeper and to harness more firepower.

"In many respects, it's a superior submarine," says independent submarine expert Norman Polmar. "We know it's at least as quiet as an improved L.A.'s. Whether it's quieter I can't say."

Polmar argues, though, the launching of the Gepard does not represent a new capability for the Russian navy.

Russian submarines traditionally have been louder than American submarines, but intelligence experts believe that starting in the mid-1980s, Russia has been advancing quieting techniques with their Akula-class submarines. The Akulas now reportedly have sound levels equal to or lower than U.S. Los Angeles and possibly the future Virginia-class submarines.

With the Gepard, reportedly the best of the Akulas, Russia is believed to have built 13 Akula-class submarines. The Gepard is of the improved Akula II series, and some experts believe Russia actually launched its first Akula II in 1996.

The U.S. Navy currently operates some 55 advanced nuclear submarines.

Important Milestone or Last Gasp?

A recent article in Moscow Rossiyskaya Gazeta, a government daily paper, claims the Gepard surpasses America's new Seawolf submarines, not yet fully operational, "in practically every way."

Still, Polmar and others say the Gepard does not represent a particularly severe challenge for the U.S. Navy. "It's meaningless, because they don't have the money to fully operate them and they have so few of them," he says.

Indeed, the Gepard is five years late in arriving. Construction was begun in 1991 and the Gepard was originally scheduled for launch in 1996. But its construction was delayed due to Russian military funding difficulties.

"It's certainly a major milestone for them that after all this time they've finally launched the bloody thing," says John Pike, a military expert who runs GlobalSecurity.org in Washington, D.C. "They went on a construction holiday, basically, 10 years ago."

But Pike notes the U.S. Navy still outclasses Russia in anti-submarine warfare (ASW), enabling it to better locate and track Russian subs.

"ASW is not simply dueling submarines. It includes aircraft, and helicopters operating from destroyers, where the United States continues to have a significant lead. And it's the computers and communications that sort of ties all of that together," he says. "One submarine alone does not decisively alter that."

Since the Cold War, the Russian fleet has fallen into serious disrepair. The launching of the Gepard, says Pike, is most significant if it reflects a new commitment in Moscow to rebuild its aging navy.

"A major challenge for the Russian navy right now is to explain why Russia has a navy," he says. "If Russia does not resume ship construction soon, five years from now they're going to wind up without a navy." — ABCNEWS' correspondent in Moscow Sergiusz Morenc contributed to this report.