Top U.S. commander in Iraq David Petraeus is calling for suspending further U.S. troop withdrawals from Iraq for 45 days after the planned pullout of five combat brigades by the end of July.

He made the appeal at the beginning of a two-day testimony on Capitol Hill.

"After weighing these factors, I've recommended to my chain of command that we continue the draw down of the surge combat forces and that upon the withdrawal of the last surge brigade combat team in July, we undertake a 45 day period of consolidation and evaluation."

He has declared "significant but uneven security progress" in Iraq, but admits that the gains are not easy to keep to make necessary a period of pause in troop drawdown.

He says the recent violence in Iraq shows that the progress is "fragile and reversible."

Also present at the testimonies is Ryan Crocker, U.S. ambassador to Iraq, who echoes Petraeus's assessment of real but fragile security gains.

Crocker says a long-term agreement the US is now negotiating with Iraq will give a needed legal framework for the continued presence of US troops.

"The agreement will not establish permanent bases in Iraq and we anticipate that it will expressly forswear them. The agreement will not specify troop levels and it will not tie the hands of the next administration."

Under Petraeus' "pause" proposal, which is favored by President George W. Bush, there will be 140,000 U.S. troops in Iraq by late July, an increase of 8,000 from January 2007.