At his press conference yesterday, President Bush seemed surprised to learn of Russian President Vladimir Putin's comments in Tehran rejecting the use of force in the Caspian region - a clear warning to the United States not to use the military option to deal with Iran's nuclear program.

In fact, Putin plainly means to use Iran as a lever against America and the West. His historic visit to Tehran this week - the first by a Russian leader since Stalin met the Allies in Tehran in 1943 - was just the latest sign.

It's bad news for us, but makes good sense for Moscow.

First off, we're not talking about any formal Russo-Iranian military alliance or anything like that (for now, anyway). After all, Russia views the Iranian regime with a great deal of suspicion. The Russians historically tend to both xenophobia and Islamophobia - and the Islamic Republic of Iran triggers both fears.

Nor is Russia thrilled about the prospects of having a rising major power (possibly with nukes) located across its soft, strategic underbelly or competing for influence in the former Soviet stomping grounds in the Caucasus or Central Asia.

Back in the 19th century, in fact, Russian forces battled with the Persians for control of Central Asia and the Caucasus - and Russia (with Britain) occupied parts of northern Persia in the early 20th century.

The Iranians aren't totally taken with the Russians, either - and all that history isn't the only reason. Putin has stopped work on (and fuel for) the nuclear reactor it contracted to build at Bushehr in Iran, and also supported some U.N. sanctions on Iran over its nuclear program.

But Iran and Russia share some major interests. For starters, both feel besieged by the United States and the West - and need ways to check what they see as encroachment on their interests.

At the very least, Putin can use Tehran to keep the United States off-balance - for example, Bush is far from the only U.S. policymaker who'll be trying to divine exactly what Putin's assertion to "not even think of using force in this region" means - and what the consequences of ignoring that admonition might be.

The Kremlin also wants to stop the U.S. missile-defense system planned for Eastern Europe. The sites are meant to counter Iranian missiles, but the Russians are still dyspeptic about the idea. Putin could use his Iran ties as a bargaining chip on "Son of Star Wars" - that is, refusing to help the West isolate Tehran unless we drop the anti-missile project.

Alternately, Russia could also use an embrace of Iran as a check on the further expansion of NATO into Ukraine or Georgia - or to demand that the Europeans get nations like the Baltic countries to accept arms limits under the the Conventional Forces in Europe treaty, reducing the potential threat to Moscow's west. Iran and Russia share another huge interest: Both regimes rely on their vast earnings from energy sales. Putin was in Tehran for a summit of the five nations that border the Caspian Sea: He wants to ensure that Russia has generous access to Caspian oil and gas.

Putin's also looking to sign up Tehran for his newest evil-genius project: an OPEC-like cartel for natural-gas supplies.

In fact, prolonging the diplomatic crisis over Iran's nuclear-weapons program helps keep Moscow's coffers overflowing - because every bit of tension in the region ensures that energy prices will stay high, maximizing the profits of exporters like Russia.

And, since high energy prices also leave Tehran flush with cash, it opens a lucrative arms market for Russia, too. Moscow has already sold Iran $1 billion in weapons - mostly air-defense systems, which would help Tehran protect nuclear sites from air attack.

Finally, the Kremlin is also looking to become a major player in the Middle East once again. (Its influence there plunged sharply once the Cold War ended.) Iran scares the Arab states - so the Arabs might court Russia's friendship as a way to contain rising Persian power.

In short, the Russians almost certainly distrust the Iranians deeply - but find them very useful. A real Russian-Iranian entente isn't a certainty, but it's certainly a new reason to worry about Putin's Russia.

Peter Brookes is a Heritage Foundation senior fellow and former US deputy assistant secretary of defense.