WASHINGTON, Feb 25 (Reuters) - Democrats on Saturday accused U.S. President George W. Bush of being casual with U.S. security as they warned of risks from a deal in which an Arab, state-owned company would gain control of six key U.S. ports.

New Jersey Gov. Jon Corzine, in the Democratic weekly radio address, urged Bush to pose tough questions during a delay of Dubai Ports World's $6.8 billion acquisition of P&O (PO.L: Quote, Profile, Research), even as a top White House official said there was no need to re-open the government's review.

"We cannot afford to let this administration be stubborn in their mistakes and casual about our security," Corzine said. "Every homeland security expert identifies protecting our nation's ports as one of our greatest unmet security challenges."

DP World said this week it would proceed with the takeover of the British P&O company -- making it the world's third largest port operator -- but not the management of the U.S. ports while it discusses security concerns.

"But what we need is not a token delay, but a serious review," Corzine said. Already lawsuits have been filed to block the deal, including by the state of New Jersey which is concerned about its Port Newark terminal.

Democrats and some members of Bush's own Republican Party have hammered the administration for approving the transaction, citing evidence that two of the Sept. 11 hijackers came from the United Arab Emirates, of which Dubai is a part, and that al Qaeda funding went via UAE banks.

The White House bristled at any suggestion that Bush was lax on national security.

"This president's highest priority is protecting the homeland. He has done so and will continue to do so, and anyone who suggests otherwise is at best ill-informed," said White House spokesman Ken Lisaius.

Bush and his administration have acknowledged they should have done more to inform Congress about the deal, but said security commitments made by DP World resolved concerns about a foreign, government-backed firm controlling U.S. ports.

"There are questions raised in the Congress, and what this delay allows is for those questions to be addressed on the Hill," Bush's National Security Adviser Stephen Hadley told reporters on Friday.

The Committee on Foreign Investment in the United States, an interagency panel that examines national security implications of foreign takeovers of U.S. assets, approved the transaction last month.

 Hadley said there were no plans to re-open the CFIUS review. "It's been completed," he said.

Bush has seen security as a winning political issue for him and his fellow Republicans, particularly ahead of the November mid-term elections. But Democrats have seized on the ports issue to raise doubts about his ability to keep America safe.

A poll this week by Rasmussen Reports showed that Democrats in Congress have edged ahead of Bush, 43 percent to 41 percent, when it comes to who Americans trust more on national security issues.

Some lawmakers have vowed to pass legislation that would block the deal, but Bush has threatened to veto the measure and said the UAE is a key partner in combating terrorism.

DP World Senior Vice President Michael Moore told Reuters on Friday the company was open to offering additional guarantees of ways to protect to U.S. ports if asked.

(Additional reporting by Caren Bohan and Caroline Drees.)    

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