By Peter Graff

BAGHDAD, Oct 20 (Reuters) - A pact to allow U.S. troops to stay in Iraq for three more years is unlikely to win approval in Iraq's parliament before the U.S. presidential election on Nov. 4, Iraqi Foreign Minister Hoshiyar Zebari said.

Zebari said Iraq still hoped to enact the pact before the end of this year when the U.N. Security Council resolution authorising the U.S. presence expires, but acknowledged difficulties reaching agreement among Iraqi political leaders.

"The aim is to sign the agreement in the fastest time possible, preferably before the U.S. presidential election on Nov. 4, but given the ... political contentions we don't think this is possible currently," Zebari told Dubai-based Al-Arabiya television.

Washington and Baghdad reached agreement on a final text of the pact last week, which would require U.S. forces to pull forces off of Iraqi streets by the middle of next year and leave the country altogether by the end of 2011, unless asked to stay.

But the pact hit a snag on Sunday when a meeting of leaders of Iraqi political blocs declined to endorse it. The cabinet is due to review it this week and then send it to parliament for approval, but without the backing of the leaders of the political blocs its fate is uncertain.

The only blocs that have endorsed the pact without reservation are the main Kurdish parties, whose members include Zebari and President Jalal Talabani.

Crucially, the Shi'ite alliance of Prime Minister Nuri al-Maliki said on Sunday it wanted to seek amendments to the draft, which had previously been described as final.

Their Shi'ite rivals, followers of cleric Moqtada al-Sadr, are deeply hostile to the pact and staged a massive street demonstration against it on Saturday.

Iraqi officials have begun discussing a "plan B", under which they would ask the United Nations for an emergency extension of the existing U.N. mandate if the pact is not ready by the end of the year.

U.S. officials have not discussed the contents of the draft publicly, although they briefed members of Congress, including the two main presidential candidates, about it on Friday.

The pact does not need congressional approval, but the administration of President George W. Bush is hoping to win broad political support for it.

Iraqi officials say the draft would allow Iraqi courts to try U.S. troops for serious crimes committed while off duty, which they have described as a major concession from Washington.

But the pact would put in place a number of safeguards to protect U.S. troops from prosecution, and some Iraqi politicians have voiced reservations about that mechanism. (Additional reporting by Raissa Kasolowsky in Dubai)

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