An effort by abortion-rights advocates to obtain White House documents regarding the morning-after pill should be rejected because a “burdensome fishing expedition” could force a constitutional showdown, government lawyers argued.

“Discovery from senior presidential advisers disrupts the functioning of the executive branch and raises serious separation-of-powers concerns,” the U.S. attorney for the eastern district of New York, Roslynn Mauskopf, wrote in court filings Friday.

The Center for Reproductive Rights wants to convince a federal judge that the Food and Drug Administration ignored its own procedures in an unprecedented effort to avoid allowing emergency contraception, marketed commercially as Plan B, be sold without a prescription. The group says it needs the White House communiqués to do so.

During one of the depositions taken in the case, an FDA official, Florence Houn, said she understood that the agency’s actions were meant “to appease the administration’s constituents.”

Center lawyers are asking a judge to force the White House to turn over email messages regarding Plan B from one of President Bush’s top domestic policy advisers, Jay Lefkowitz, as well as other documents they hope will illustrate their assertion.

The lead counsel for the plaintiffs, Simon Heller, called the government’s filings an attempt to intimidate the court.

“We’re not intruding on any presidential power because there’s no presidential power to determine the prescription status of drugs,” he said.

Government lawyers are invoking Supreme Court precedents ranging from Marbury v. Madison in 1803 to one set two years ago when the White House successfully fended off a lawsuit seeking to find out who helped Vice President Cheney set America’s energy policy.

A White House spokesman, David Almacy, declined to comment, saying the Justice Department’s court filing speaks for itself.

Plan B is essentially a heavy dose of hormones that prevents an egg from being fertilized. It is politically sensitive because groups opposed to abortion say that Plan B is tantamount to ending fetal life.

Outside the courts, the Plan B dispute has left the FDA — which regulates almost a quarter of consumer products — without a commissioner for much of the Bush presidency.

The nomination of the president’s latest choice, Andrew von Eschenbach, is being held by Senators Clinton and Murray until the FDA takes action on Plan B after a previous nominee — who has since resigned on unrelated allegations of financial impropriety — broke his promise to take action on the drug.

The Government Accountability Office, a nonpartisan investigative arm of Congress, found that senior FDA officials decided to reject Plan B before the vast majority of its own scientific panel could recommend that it be approved.

A deal that would let Plan B be sold without a prescription to women 18 and older is possible soon, the drug’s manufacturer said recently, but Dionne Scott of the Center for Reproductive Rights said her group would continue to sue until all women get over-thecounter Plan B access.