"There is a great reluctance to engage further in the drafting process," Gates told reporters, according to Reuters. "I don't think you slam the door shut, but I would say it's pretty far closed."
The status of forces agreement that provides a legal basis for U.S. troops in Iraq would replace the current U.N. mandate, which expires at the end of the year.
The draft would require U.S. troops to leave by the end of 2011 unless Baghdad asks them to stay longer. It also would allow Iraqi courts to try U.S. service members accused of serious crimes while off duty, marking the first time foreign troops would function under the authority of the newly elected government in Baghdad.
Iraqi Prime Minister Nouri al-Maliki has shown the draft to Iraqi political leaders as the next step in getting parliamentary approval. But some politicians have expressed reservations over the details.
"The cabinet has agreed that necessary amendments to the pact could make it nationally accepted," government spokesman Ali al-Dabbagh told Reuters after a cabinet meeting on Wednesday.
"The cabinet will continue its meetings (in coming days), in which ministers will give their opinions and consult and provide the amendments suggested. Then this will be given to the American negotiating team."
Kurdish groups have so far supported the deal. But al-Maliki's rivals, supporters of Shiite cleric Muqtada al-Sadr, strongly oppose the pact, as does the leadership of mainly Shiite Iran, saying it would give U.S. forces a long-term foothold in the region, Reuters reported.
A senior, non-Shiite government source said the delay was prompted by Shiite politicians under Iranian pressure, according to the news agency.
"It seems there was a (Shiite) alliance decision to reject it," he said. "I can only explain these Shiite delaying tactics by Iranian pressure. There's no other explanation, especially as it's the Shiites who negotiated it in the first place."