(Adds foreign fighters, Halabja anniversary)

By Paul Tait

BAGHDAD, March 16 (Reuters) - U.S. Republican presidential candidate John McCain arrived in Iraq on Sunday to assess the success of a U.S. troop build-up that he has strongly backed, part of a week-long trip to the Middle East and Europe.

He is scheduled to meet Iraqi leaders and U.S. military officials, said U.S. embassy spokeswoman Mirembe Nantongo. He is visiting as a member of a fact-finding mission for the U.S. Senate Armed Services Committee.

McCain, who will be the Republican choice in November's presidential election, and Senate allies Joe Lieberman of Connecticut and South Carolina Republican Lindsey Graham will also visit Israel, Britain and France.

Analysts see the trip as a chance for McCain to show off his knowledge of foreign policy and military affairs while Hillary Clinton and Barack Obama fight out a bitter Democratic nomination process at home.

While acknowledging that leaders like British Prime Minister Gordon Brown and French President Nicolas Sarkozy might see the trip as a chance to size him up as a potential president, McCain has said he is not travelling as a candidate.

The visit is his eighth to Iraq since U.S.-led forces invaded Iraq in March 2003 to topple Saddam Hussein.

McCain, a former Navy pilot and Vietnam War hero, supported going to war but was a vocal critic of how the war was conducted until an extra 30,000 troops were deployed last year as part of a new counter-insurgency strategy.

His political standing has risen and fallen to some degree depending on whether the war has been going well or badly.

McCain said last week that the quickest way to bring the war to a conclusion was by "continuing the surge". Obama and Clinton favour bringing home U.S. troops as soon as possible.

On his last visit in April 2007, McCain made an embarrassing gaffe, saying after a heavily protected visit to a Baghdad market that the American people were not being told the "good news" about the war in Iraq.

Iraq was still gripped by widespread sectarian violence at the time and the area he had been visiting was very dangerous. McCain later admitted he had misspoken in his upbeat assessment.

RECONCILIATION CONFERENCE

Attacks across Iraq have fallen by 60 percent since last June, when the troop build-up was completed. There has been a spike in violence since January, with an upsurge in suicide bombings linked to al Qaeda.

The U.S. military says most of the suicide bombers tend to be foreign fighters.

Citing a case study of 48 foreign fighters captured in Iraq in the last four months, U.S. military spokesman Rear Admiral Greg Smith said on Sunday:

"They tend to be a single male. The average age is 22. Most of these men have no military experience. They primarily (draw) a low wage income. They are taxi drivers and construction workers... Most of these terrorists were from large families who found it hard to be noticed."

Overall levels of violence are down, which U.S. commanders attribute to the extra troops, the growth of mainly Sunni Arab anti-al Qaeda neighbourhood patrols, and a ceasefire called by Shi'ite cleric Moqtada al-Sadr for his Mehdi Army militia.

Washington has been urging Baghdad to take advantage of the improved security to press ahead with political measures aimed at reconciling majority Shi'ite and minority Sunni Muslims.

While some progress has been made on key laws, the Shi'ite-led government of Prime Minister Nuri al-Maliki remains deadlocked on others like a revenue-sharing oil law for Iraq's reserves of crude, the world's third largest.

Late on Saturday Maliki announced that a national reconciliation conference would be held this week. Government spokesman Ali al-Dabbagh said political parties and tribal and religious leaders would take part in the two-day gathering.

Kurds in the northern Iraqi town of Halabja meanwhile held sombre ceremonies marking the 20th anniversary of a poison gas attack by Saddam Hussein's forces in 1988 that killed 5,000 people, an incident which achieved world-wide notoriety. (Additional reporting by Ross Colvin and Mohammed Abbas in Baghdad)

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