* Ruto's trial starts Tuesday, Kenyatta's in November
* Kenyatta: could halt cooperation if trial dates overlap
* Tentative schedule has trials coinciding for five weeks
* Kenya role as West's ally against militant Islam at stake
By James Macharia
NAIROBI, Sept 9 (Reuters) - Kenya's president said it could be forced to halt cooperation with the International Criminal Court if it requires both him and his deputy - both charged with crimes against humanity - to attend hearings in The Hague at the same time.
The West has urged Nairobi to cooperate with the ICC because it failure to do so would undercut contacts with Nairobi seen as crucial to its role as a regional bulwark against militant Islam. Kenya is also a big recipient of U.S. and European aid.
Diplomats have said until now that they expect President Uhuru Kenyatta and his deputy, William Ruto, to live up to pledges to cooperate. But Kenyatta's new comments could raise concern about a change of heart.
Kenyatta's ICC trial starts in November while Ruto left Kenya on Monday to attend Tuesday's first hearing.
Kenyatta and Ruto, who won an election in March, are accused of leading their respective ethnic groups to fight each other in violence that followed Kenya's disputed 2007 election, when they were in rival political camps.
Failure to cooperate could, in a worst case, prompt an arrest warrant that might in turn incur penalties from generous Western donors against east Africa's biggest economy, although diplomats have said they think that is an unlikely scenario.
"If you want us to continue to cooperate with the ICC process let me make it crystal clear that when Ruto is at The Hague I will be here and when I am at The Hague he will be here," the president told a prayer rally on Sunday.
He said he was speaking "in my capacity as the president of this republic, not as an accused person", addressing supporters attending the event to pray for the two men before trial.
Kenyatta had told a rally on Saturday in Eldoret near Ruto's political stronghold that Kenyans should not be worried even if both men were away. Sunday's comments indicated a tougher line.
Last week, parliament, dominated by Kenyatta's supporters, voted to pull out of the ICC's jurisdiction, a move that would take a year to implement and would not affect trials in motion, but has raised some concerns about Kenyan commitment.
The ICC is already facing growing opposition in Africa, where it is seen as biased for having only charged Africans.
For the ICC, Kenyatta's statement raises the stakes for a court trying its first sitting president, posing a challenge over whether it would back down and change the trial dates.
A tentative trial schedule published on the ICC website requires both leaders to be at The Hague for five consecutive weeks between Nov. 12 and Dec. 13.
GOVERNMENT BY SKYPE?
The ICC's Gambian prosecutor, Fatou Bensouda, said in a press conference televised from the Hague that the decision on the schedule for the trials is determined by the court's judges.
"Their presence here at the same time is a matter for the judges to decide, and not the prosecutor," she said. "I believe the judges will at the appropriate time make the appropriate decision."
Speaking immediately after Bensouda, Ruto's lawyer Karim Khan said he planned to make an application to the judges "in due course" to have the president and deputy president appear at the court on alternate dates.
ICC Registrar Herman von Hebel had earlier said the court expected Kenya to continue cooperating even if it withdrew from the court's jurisdiction.
The Rome Statute that established the ICC requires the accused to be present throughout during their trial. Both men have attended pre-trial hearings up to now.
During the election campaign, Kenyatta had to fend off jibes by his main rival for the presidency, former prime minister Raila Odinga, that he could not govern and run Kenya at the same time, saying it would mean government by Skype.
Politicians from both sides of the divide have expressed concern that in the absence of Kenyatta and Ruto, Kenya could face a leadership vacuum, slowing down the decision-making process in a country emerging from an election that went peacefully but again exposed ethnic and tribal divisions. (Reporting by James Macharia; Editing by Edmund Blair and Mark Heinrich)