(Adds Maliki adviser in paragraphs 10-12)

By Mussab Al-Khairalla and Waleed Ibrahim

BAGHDAD, Sept 16 (Reuters) - Iraqi cleric Moqtada al-Sadr's political movement has no immediate plan to bring down Prime Minister Nuri al-Maliki's government despite pulling out of his ruling Shi'ite Alliance, a spokesman said on Sunday.

Sadr's bloc withdrew from Maliki's parliamentary coalition on Saturday, leaving him with the support of only about a half of the legislature's 275 lawmakers.

"We have many reservations about Maliki's government but we haven't discussed a vote of no confidence yet because it's still too early to talk about this matter," said Salah al-Ubaidi.

Maliki can count on the backing of two Shi'ite Islamist parties and the two main Kurdish parties in parliament, and could probably survive with the support of a handful of independent lawmakers.

But the Sadr bloc's withdrawal further weakens his coalition, which even before the defection had failed to push through laws aimed at reconciling Iraq's warring majority Shi'ite and minority Sunni Arabs.

"Maliki lost an important ally ... an ally which helped him reach power," said Dhafir al-Ani, a parliamentarian from the main Sunni Arab bloc, the Accordance Front, which pulled its six ministers from Maliki's cabinet last month.

"The government is in a fragile and weak position. The allies of yesterday, today are adversaries."

Sadr, who led his Mehdi Army militia in two uprisings against U.S. forces in 2004, was instrumental in getting Maliki, a fellow Shi'ite, appointed prime minister in May last year.

SADR GRIEVANCES

Sadr's political bloc has raised a host of grievances in the past, including Maliki's refusal to set a timetable for the withdrawal of U.S. forces from Iraq.

The government has made no official comment on the movement's withdrawal from the ruling alliance, but a senior adviser to Maliki said the government was not about to fall.

"I don't see this withdrawal weakening the government," Sadiq al-Rikabi told Reuters.

"All attempts to overthrow the government have failed because the government is supported by a very strong political and parliamentary bloc."

Kurdish politician Abdul-Khaliq Zengena, whose party is part of Maliki's remaining parliamentary coalition, criticised the Sadr bloc's move.

"It is not constructive and hampers progress," he told Reuters. "Politicians must always calculate these moves carefully and see if it's in the interest of the political process and a return to stability."

The Sadr movement's withdrawal from the Shi'ite Alliance in parliament was not unexpected after the anti-American cleric ordered his six ministers to quit the cabinet in April.

The Accordance Front withdrew its ministers after saying the prime minister had ignored their demands.

Ani said Sadr's supporters had been in contact with his bloc a few weeks ago to discuss a parliamentary challenge to Maliki's government.

"I believe now the Sadrists will be very enthusiastic to do such a thing, to go to parliament and ask for a vote of no confidence," he said. (Additional reporting by Khaled Farhan in Najaf)

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