Washington ? Russian President Vladimir Putin’s sense of besiegement is deepening and pushing him to take an ever-harder line against neighbors and opponents. Western plans to moderate Putin’s behavior through conciliation and engagement have failed. They should now be reassessed.

Neither a crushing political defeat in Ukraine’s December elections nor a friendly session of tough-love diplomacy with President Bush in Slovakia last month convinced Putin to change tone, much less gears.

The Russian leader’s defiant demeanor at a joint news conference after the summit with Bush in Bratislava hinted at an assertive determination to do things his way come what may. That mood was confirmed in blood by the killing of Chechen rebel leader Aslan Maskhadov by Russian security forces on Tuesday.

“This is a message to the entire region, and probably the world, that Putin will not pursue any negotiated settlement to the conflict with the Chechens,” says a Washington-based diplomat from a former Soviet republic. “He has eliminated any alternative to Russian military conquest as an acceptable outcome for him.”

Russian forces chose to kill the surrounded Maskhadov with a grenade instead of trying to capture him. Coming only weeks after Putin’s meeting with Bush, the killing is an operational setback as well as a public-relations problem for Washington.

It derails a subtle behind-the-scenes effort by the Bush administration to nudge Putin toward seeking a political solution in Chechnya — an outcome that only Maskhadov may have been able to deliver, in the view of some U.S. officials.

Maskhadov, the president of the Chechen republic’s underground separatist government since 1997, portrayed himself as a willing negotiator who rejected the terrorist outrages of the brutal warlord Shamil Basayev. The Russians, however, accused Maskhadov of being a front man for Basayev and his allies in al-Qaida’s terrorist network.

Maskhadov’s death ends that debate for all practical purposes. Both Russian dissidents and Chechen guerrillas predict that the rebellion will now be a fight to the finish that will be marked by even more horrendous terrorist acts.

Bush’s need for Putin’s help in the global war on terrorism gave him little room to pressure the Russian on Chechnya. But Bush has been more restrained than was Bill Clinton in backing Moscow on the issue of Chechen separatism, and the president let his aides keep lines of communication open to the Maskhadov camp.

Bush’s instinctive liking for Putin seems to endure: For one thing, neither of them does nuance. “One cool dude” is the way Bush described Putin to another leader shortly after first meeting him in June 2001. The Russian president is “Vladimir” when they talk and “Puty” on Bush’s long list of nicknames.

Before the February meeting in Bratislava, more skeptical readings of Putin circulating at the State Department had not been absorbed by the White House. That should no longer be the case.

It is not just Chechnya. One leader who talked with Putin in recent weeks recounts that the Russian launched a long tirade against the Organization for Security and Cooperation in Europe (OSCE), which was established in 1975 to monitor security, human rights, democracy and other issues.

NATO is “a serious organization” and presents no problems for Russia, Putin said, according to the surprised European official. It is the OSCE that is intent on destabilizing Russia now, interfering in its former sphere of influence by encouraging democracy in Ukraine, Georgia and elsewhere, the Russian leader maintained.

This paranoia has led Putin to try to block funding for the 55-member body. The West must present a united front against this disastrous course, and against other self-defeating lurches of retrenchment and self-isolation by Putin.

German Chancellor Gerhard Schroeder is best positioned to lead in establishing and communicating policy red lines to Putin. It was Schroeder who reassured Putin in December that European mediation in Ukraine was not directed against Russia and should not be opposed, according to a reliable account.

But Schroeder will need strong encouragement, and perhaps prodding, from Washington, London and Paris to get him to take a firmer line with Putin. Only if Schroeder is persuaded that Putin is choosing self-defeating options will the chancellor intervene.

Not long before going to Bratislava, Bush asked a foreign leader two vital questions that are late in coming but nonetheless welcome. They were, as relayed to me in paraphrase: Was I too trusting in my first meeting with Putin? Did I overinvest in him?

To ask those particular questions is to begin to answer them, correctly. If Putin won’t change gears, Bush and his partners must.

— Jim Hoagland is a columnist for Washington Post Writers Group.