BUCHAREST, Romania — With President Bush headed to what is likely to be his final summit conference with President Putin of Russia, the North Atlantic Treaty Organization on yesterday provided the show of support Bush sought for the missile defense plan the Russian leader has vehemently opposed.

The alliance also renewed its political and military support for the American-led war in Afghanistan; welcomed two new members, Croatia and Albania; and opened the door to eventual membership to Montenegro and Bosnia-Herzegovina.

With the 12 members admitted in the nearly two decades since the end of the Cold War and those on the formal path toward membership, NATO is demonstrating a dramatic evolution eastward. Figuratively and literally, it is moving away from its post-World War II roots as an alliance of America, Canada, and the major powers of Western Europe erecting a defense network against the nation of the Soviet-led Warsaw Pact.

A day after it became clear that the alliance would balk at meeting Mr. Bush’s demand to put Ukraine and Georgia on the first rung of a ladder intended to lead toward membership, the alliance instead said that the countries would eventually be allowed in — and that NATO foreign ministers would consider the matter again in December.

The summit, which marked the alliance’s 59th anniversary, dealt a setback to Macedonia’s hope that it would be admitted with Albania and Croatia. NATO actions require the consent of all members, and Greece has long objected to Macedonia’s name, which it says is in conflict with a region of Greece that bears the same name. Throughout the day, Mr. Bush, Secretary of State Rice, and the national security adviser of the administration, Stephen Hadley, and other American officials sought to present the summit as an unqualified success for the administration.

At times it was easier than others.

The support for the missile defense system, which the administration wants to build in the Czech Republic and Poland, went the administration’s way.

But Mr. Bush had lobbied hard, first privately and then in public, in recent weeks to start Ukraine and Georgia on the road to NATO membership. NATO members Germany and France opposed the move, with Chancellor Merkel of Germany leading the argument that the two would-be members had not done enough to reform their politics and military forces.

In addition, Mr. Putin, who arrived in Romania yesterday to take part in a Russia-NATO meeting on Friday, opposes giving membership for the two countries, which were part of the Soviet Union and now sit on Russia’s southern border.

Mr. Bush, who is flying Friday to Zagreb, Croatia, for an overnight visit, is meeting with Mr. Putin this weekend at the Russian Black Sea resort of Sochi, with the missile defense issue one of the top items on the agenda. Mr. Putin leaves office on May 7, and Bush is scheduled to meet with his successor, Dmitri Medvedev.