The government has a right to secrecy, Mr Cheney says

The Bush plan opened some public land to drilling - most controversially the Alaskan National Wildlife Refuge - and offered tax incentives to energy firms.

The GAO now wants Mr Cheney to disclose the content of meetings between Enron and government officials during the formulation and implementation of the plan.

Enron, like many other large energy firms, welcomed the Bush administration's policy.

Robust defence

In remarks on US TV over the weekend, Mr Cheney defended official secrecy on a number of counts.

"Now, the fact is, Enron didn't get any special deals," Mr Cheney said on ABC.

"Enron's been treated appropriately by this administration."

To Fox News, Mr Cheney argued that confidentiality was sometimes unavoidable.

"What we've told GAO we won't do is make it impossible for me or future vice presidents to ever have a conversation in confidence with anybody without having, ultimately, to tell a member of Congress what we talked about," he said.

"Can you imagine an FDR or Teddy Roosevelt, in the midst of a grave national crisis... trading away a very important fundamental principle of the presidency?"

Court battle looms

Now that Mr Cheney has expressed his willingness to stand firm, the stage is set for a confrontation between the GAO and the White House.

The GAO, which was asking for the documents even before Enron's collapse, has stepped up its campaign in recent weeks.

Its head, David Walker, said on Sunday that it was "highly likely" that the office would take legal action against Mr Cheney.