WASHINGTON — U.S.-led coalition forces would leave Iraq if a new interim government should ask them to, Secretary of State Colin Powell said Friday, but such a request is unlikely.

Powell said the United States believes that a U.N. resolution passed last year and Iraqi administrative law provide necessary authority for coalition forces to remain even beyond the scheduled June 30 handover of the government to Iraqis.

"We're there to support the Iraqi people and protect them and the new government," Powell said at a news conference with his counterparts from other Group of Eight nations preparing for an economic summit next month. "I have no doubt the new government will welcome our presence and am losing no sleep over whether they will ask us to stay."

But were the new government to say it could handle security, "then we would leave," Powell said.

While those discussions were taking place, American tanks made their deepest incursion yet Friday into Najaf, the stronghold of radical cleric Muqtada al-Sadr. Apparent gunfire slightly damaged one of the Islamic Shiites' holiest shrines, prompting calls for revenge and even suicide attacks.

Echoing Powell, L. Paul Bremer, the top U.S. administrator in Iraq, told a delegation from Iraq's Diyala province Friday that American forces would not stay where they were unwelcome.

"If the provisional government asks us to leave, we will leave," Bremer said, referring to the interim Iraqi administration due to take power June 30. "I don't think that will happen, but obviously we don't stay in countries where we're not welcome."

Undersecretary of State Marc Grossman had told the House International Relations Committee on Thursday that although it was unlikely, the Iraqi interim government could tell U.S. troops to leave. But Lt. Gen. Walter Sharp, who was also at the hearing, contradicted his statement, telling the panel that only an elected government could order a U.S. withdrawal.

White House spokesman Scott McClellan told reporters Friday that the Iraqi people still want help from the United States and coalition forces to provide security.

"Iraqi security forces are not fully equipped and trained to provide for their own security and defend their country against terrorists," McClellan said. "And so, after the transfer of sovereignty on June 30, we expect to continue to partner with the Iraqi forces to improve the security situation."

British Foreign Secretary Jack Straw said at the news conference with Powell that stability in Iraq would not be served by an abrupt withdrawal.

"But were the government that takes over to ask us to leave, we would leave," Straw said. Britain is the main force other than the United States in the U.S.-led military coalition that brought down Iraq's authoritarian government last year and is trying to restore calm in the aftermath.