BAGHDAD, May 1 (Reuters) - Iraq's main Sunni bloc is considering quitting the Shi'ite-led government because it believes the concerns of Sunnis are not being addressed, members of the bloc including the vice president said on Tuesday.

Some members of the Sunni Accordance Front have been urging the bloc for several months to pull out of Shi'ite Prime Minister Nuri al-Maliki's cabinet, partly over accusations that reconciliation with minority Sunni Arabs has moved too slowly.

But frustration has grown in recent weeks, members said.

The bloc has six ministers in the government and a withdrawal would be a blow to Maliki and raise questions about how representative his administration would remain.

A pullout would not be enough to topple Maliki, as he would still have a majority in parliament through his ruling Shi'ite Alliance and a coalition of Kurdish parties. The Accordance Front has 44 seats in the 275-member parliament.

Six ministers from the movement of fiery Shi'ite cleric Moqtada al-Sadr quit the government last month in protest over Maliki's refusal to set a timetable for withdrawing U.S. troops.

"We are serious in withdrawing if nothing new happens with progress in the political process," Adnan al-Dulaimi, head of the Sunni bloc, told Reuters from Amman where he was on a visit.

"Reconciliation the government speaks of is only for conferences and speeches. No results can be seen on the ground."

"STUMBLING POLITICAL PROCESS"

Vice President Tareq al-Hashemi, a senior member of the bloc, told Reuters the Front would make its position known soon.

"We are very serious in taking a real unified stance over a possible withdrawal," said Hashemi, who discussed the issue with U.S. President George W. Bush in a telephone call on Sunday.

Washington has set Iraq's government benchmarks that it wants to see progress on by September, and which U.S. officials believe will be crucial to bringing Sunni Arabs, the backbone of the insurgency, more firmly into the political process.

It wants parliament to delay a two-month summer recess due to start in July to pass laws on sharing Iraq's oil wealth, easing a ban on former members of Saddam Hussein's Baath party holding office, and paving the way for provincial elections.

Hashemi's office said in a statement on Monday that Hashemi and Bush had discussed Iraq's "stumbling political process" in their telephone conversation.

Other bloc members have said the Accordance Front should stay in the government, arguing they can achieve more by remaining part of the political process, something noted by Sadiq al-Rikabi, a senior adviser to Maliki.

"We know key elements of the Accordance have a very positive position on the government and the information we have is very different to what we see in the media," Rikabi told Reuters.

Maliki, a Shi'ite Islamist, insists the government is making progress toward reconciliation between majority Shi'ites and Sunni Arabs who were dominant under Saddam Hussein.

He also says a 10-week old security crackdown in and around Baghdad is targeting gunmen regardless of sect.

Mahmoud Othman, an independent Kurdish lawmaker in Baghdad, said a pullout of the Accordance Front would hurt Maliki.

"The government will still be able to function, it will still have a majority in parliament but it will be very weakened," Othman said. "The Sunnis are part of the government but they feel they are not real partners."

(Additional reporting by Mussab Al-Khairalla and Ibon Villelabeitia)