The high-stakes week of diplomacy comes as Washington seeks more sanctions against Tehran and worries about the health of democratic reforms in Moscow.

Bush will host his French counterpart at the White House on Tuesday for an official dinner, then squire him on Wednesday to the Mount Vernon estate of the first US president, George Washington. It is Sarkozy's first official trip to the US. The two leaders were expected to celebrate the 250th anniversary of the birth of the Marquis de Lafayette, the French soldier and diplomat who played a key role in the American revolution.

Merkel was to get an even juicier diplomatic plum, arriving Friday for a weekend stay at Bush's beloved "Prairie Chapel" ranch in Texas, a prize reserved for especially close allies.

Merkel moved swiftly to mend ties that had deteriorated between Bush and her predecessor, Gerhard Schröder, when she took power two years ago. But US diplomats say small differences have started to emerge on issues ranging from Iran's nuclear program to Afghanistan and Kosovo, where Merkel's cautious, consensual approach has begun to grate in Washington.

Bush and his guests will have a full diplomatic plate: "Iraq, Lebanon, Syria, Middle East peace process, Kosovo, Burma, Afghanistan and Darfur, Trade, NATO, transatlantic relations, climate and energy security" are also on the menu, according to White House spokesman Gordon Johndroe.

But the issues of Iran -- which denies US charges that it seeks nuclear weapons and has bucked international pressure to freeze uranium enrichment -- and Russia -- including Moscow's relations

with Tehran and its cloudy political future -- will dominate.

Russia and Iran worries

US officials worry that term-limited Russian President Vladimir Putin, who has suggested he may become prime minister after stepping down next year, is backing away from democratic reforms.

Bush, who spoke to Putin by telephone two weeks ago, "wants to hear from both Sarkozy and Merkel about their recent meetings with Putin, and how they think things are developing with our Russian friends," said Johndroe.

The US president, who recently imposed new US sanctions on Iran, wants the UN Security Council to approve a third round of its own punitive measures and needs France -- a permanent council member -- and Germany to be on board.

US officials say Bush hopes that Russia, angry at Washington over plans to deploy a missile defense system in its eastern European backyard, will not oppose such a move.

The head of the UN atomic watchdog agency, Mohamed ElBaradei, and EU foreign policy chief Javier Solana are due to report back on Iran's nuclear program in November, said Johndroe.

"If their reports are not positive, then we are headed to a third sanctions regime," he said, adding that "any discussion of issues before the UN Security Council is going to lead to 'where does Russia stand?'"

Johndroe warned against characterizing this week's two meetings as summits on Iran, but said the issue of the Islamic republic's suspect atomic drive "will get its fair share of attention."

The meetings also highlight the evolving relationship between the Bush administration and France and Germany, which fiercely opposed the March 2003 US-led invasion of Iraq, but have since changed leaders.

On good terms, so far

Bush and Merkel "have a very good rapport," Johndroe said. "They get along quite well. They speak to each other very honestly and openly, and that enables them to solve problems."

Bush and Sarkozy have also "been getting along quite well," he added. "They see eye to eye on the need for France and the United States to be have good relations. Friends can, of course, disagree."

As for critics who say Sarkozy is overly pro-American, "it's very fashionable to be anti-American, so it's not surprising that some would say that," Johndroe said. "But at the end of the day, there is a strong desire (in France) to have solid relations."

Sarkozy's advisors say the French leader knows the risks he is running being so friendly with an unpopular US president.

In Paris, opposition socialists have sought to portray Sarkozy as a "Bush poodle," a sobriquet once reserved for former British Prime Minister Tony Blair.