Barack Obama campaigned on the promise of "change," but one change the president-elect may be planning on - not deploying a US missile defense in Eastern Europe - would be a big mistake.

Indeed, it's exactly the type of about-face that nations like Russia, Iran and North Korea hope for from the incoming administration.

Worse, it will likely be seen abroad as knuckling to Russian bullying.

Two weeks ago, just a day after the US elections, Russian President Dmitry Medvedev made a virulently anti-American speech - his first major address since taking office this spring and arguably the first foreign "test" of the president-elect.

Amid other ranting, Medvedev demanded that the United States back off on its planned missile-defense bases in Poland and the Czech Republic.

If the deployment goes ahead, Medvedev warned, Moscow will place short-range missiles in Kaliningrad - a Russian enclave nestled between NATO members Poland and Lithuania.

A few days after the Medvedev speech, a senior Obama aide came out after a phone call between the president-elect and Polish President Lech Kaczynski saying that Obama had "made no commitment on" missile defense.

Ugh. That's not a certain retreat by Washington in the face of Moscow's threats, but it's a very troubling start for the Obama team on a key national-security issue.

Going wobbly caused heartburn in Warsaw and Prague, where both governments went to the mat to get approval for the missile-defense deal - and glee in Moscow, Tehran and Pyongyang.

What rogue doesn't love a whiff of wobbliness?

And the stakes rose just days later, when The Wall Street Journal reported that Russia is now in talks to deploy missiles in Belarus, which could be bore-sighted on targets across Europe.

(Belarus' motive? It's probably looking for Russian help on energy supplies and financial credits - or, if Europe wants to bribe it to reject the missiles, for an easing of EU economic sanctions imposed over human-rights issues.)

The next step in this ongoing lesson for the president-elect came Friday - when French President Nicolas Sarkozy called for a halt to European missile defense until more talks can be held.

Sarkozy's words, at a European Union-Russia summit, were a clear sop to fellow attendee Medvedev - at the expense of the United States and the president-elect. (Shamefully, the EU is re-engaging Russia despite Moscow's failure to meet the EU six-point peace plan for Georgia.)

But the issue isn't just bullying - there's the policy, too. This system is designed to defend against the Iranian missile and nuclear threat - which is growing fast.

Just last week, Tehran tested a two-stage, solid-fuel ballistic missile - whose 1,200-mile range would let it hit all of the Middle East and parts of southeastern Europe.

If reports of the Iranian test are true, this would be Tehran's first successful test of a multistage rocket - which would put it on track for launching missiles to ever-increasing ranges, including intercontinental distances. The test also showed advances in Iran's basic rocketry science, moving beyond liquid fuels to a more reliable solid-fuel rocket motor.

The last thing we need is to look "soft" on Iran's nuclear and missile programs.

North Korea's leadership, meanwhile, would also be tickled pink over the demise of a missile-defense initiative - which can only add to the value of their nuclear and missile programs.

Let's be clear: We're talking about missile defense here - systems meant to protect our homeland, our allies and friends and US troops against offensive threats.

The Bush administration decided that leaving us deliberately vulnerable was foolish - and has moved to deploy systems against an array of missile threats.

And rightly so: In a dog-eat-dog world, any power that seems weak invites provocation, blackmail, coercion or even aggression.

Missile defense gives policy makers choices beyond massive retaliation - and is one of our few reasonable options to protect ourselves and our interests against the growing threat of missiles and weapons of mass destruction.

For Obama to give in to Russian threats wouldn't just make him look weak in the eyes of our enemies and friends; it would weaken America's security, too.

Peter Brookes, Senior Fellow at the Heritage Foundation, is a former deputy assistant secretary of Defense.