President Bush on Tuesday vowed full support for Ukraine and Georgia's NATO aspirations, saying Russia would have no veto over the ex-Soviet states' membership bids.

In Kiev ahead of a NATO summit, the president said he would work "as hard as I can" to overcome Moscow's objections and concerns from some in the trans-Atlantic military alliance about starting the admission process for the two nations.

"Your nation has made a bold decision and the United States strongly supports your request," Bush told Ukrainian President Viktor Yushenko two days before NATO leaders meet in Bucharest, Romania to decide on a so-called "membership action plan," or MAP, for both Ukraine and Georgia.

"In Bucharest this week, I will continue to make America's position clear: we support MAP for Ukraine and Georgia," he said after talks with Yushenko. "My stop here should be a clear signal to everybody that I mean what I say: It's in our interest for Ukraine to join."

A membership action plan outlines what a country needs to do to win an invitation for full NATO membership.

With nine former Soviet bloc countries already NATO members, Russia is opposed to Ukraine and Georgia even starting the process, fearing a further loss of influence in two more Soviet-era Warsaw Pact neighbors. A senior Russian diplomat warned Tuesday that Ukraine's accession to NATO would cause a "deep crisis" in relations with Moscow.

Some NATO allies, notably France and Germany, are reluctant to give Ukraine and Georgia the precursor to membership, saying they are not ready. But they also fear upsetting already strained ties with Russia, a major supplier of energy to Europe.

"France will not give its green light to the entry of Ukraine and Georgia," the French prime minister, Francois Fillon, said in a radio interview Tuesday. He said potential NATO membership by the two countries could upset the balance of power between Europe and Russia.

But Bush praised Ukraine's democratic and military reforms, and noted that Ukraine "is the only non-NATO nation supporting every NATO mission." Ukraine has sent troops to Afghanistan, Kosovo and Iraq. He said a positive decision is "in the interests of our organization."

Bush's forceful backing sets up an internal showdown in the alliance. The president said he and his top aides would continue to lobby all NATO members.

"Every nation has told me Russia will not have a veto over what happens in Bucharest. I take their word for it," he said, adding: "I wouldn't prejudge the outcome just yet, the vote will be taken in Bucharest."

The pro-western Yushenko said he was optimistic his country would get the nod from NATO and discounted opposition from some in Ukraine to moving to join the alliance.

"I am sure that we will receive a positive signal in Bucharest and that's the spirit that we are going there with," he said, sitting beside Bush at a news conference in a narrow room with a high ceiling decorated with ornate molding.

Bush's unequivocal support for Ukraine and Georgia adds another complication to ties with Russia already strained over U.S. plans to build a missile defense shield in Europe.

Bush meets Sunday with outgoing Russian President Vladimir Putin at the Black Sea resort of Sochi and said it was a "misperception" that the United States might soften its push to get Ukraine and Georgia into NATO if Russia backs off opposition to the shield.

"There's no trade-offs. Period," Bush said. "As a matter of fact, I told President Putin that in my phone call to him recently."

White House officials have expressed some optimism that the two leaders could reach a deal on the bitter missile defense dispute during this weekend's talks.

Bush himself was cautiously optimistic. "Obviously, we've got a lot of work to do to allay suspicions and old fears, but I think we're making pretty good progress along those lines," he said.

He repeated his stance that the missile-defense plan is meant to counter a threat from a rogue Middle East nation and poses no threat to Russia. Still, Putin has heard that many times before and remains wary.

For months, Putin has stepped up anti-American rhetoric, demanding that the U.S. abandon the plan to base missiles in Poland and the Czech Republic, two former Soviet satellites. He has complained it would upset the balance of power and was aimed at weakening Russia, charges the United States has denied repeatedly.

Ukraine meant to showcase its best side during Bush's visit, in hopes of a boost ahead of the NATO summit. A formal welcoming ceremony for Bush featured the playing of national anthems and a parade of high-stepping military men in long, belted dress coats with fur collars. Both are typical of the greetings Bush gets all over the world, but these arrival rites took on particular importance here because of Ukraine's NATO drive.

Ukraine had long flirted with joining the alliance, but it started taking real steps toward meeting its military and political standards only after Yushenko became president in the wake of 2004 street protests, called the Orange Revolution.

Since then, Ukraine has gained a vibrant opposition, a robust media and has held a series of clean elections. It has also set out to modernize its Soviet-style military, including creating an all-volunteer army and changing troop deployment and training to meet NATO standards. Kiev abandoned customs and practices that date to Soviet and even Czarist Russia times, such as using soldiers for kitchen duty and outfitting them in cumbersome footwear. It also sought to prove itself by deploying troops to Iraq in 2003-2005 and sending peacekeepers to Kosovo and Lebanon.

Remaining problems, however, range from rampant corruption to constant political turmoil, which has caused a stream of government shake-ups and early elections over the past years.

"In my opinion, there are no alternatives to the idea of collective security and I believe that collective responsibility for security policy, or defense policy, is the best response to the challenges that currently exist in society and in the international system," Yushenko said.