House Democratic Leader Nancy Pelosi demanded an ethics investigation Thursday into the passage of deficit-reduction legislation that President Bush recently signed, a new twist in an episode of Capitol intrigue that blends election-year politics and questions of constitutional law.

"Republican leaders chose to ignore House rules, precedent and even the Constitution itself" in sending the politically charged measure to the White House, said Pelosi, D-Calif.

She said the legislation was defective because it had cleared the two houses in different forms, and added that Speaker Dennis Hastert, R-Ill., "knew full well this was an invalid bill."

Republicans, citing an 1894 court precedent, say the measure is valid because top House and Senate leaders put their own signatures on the bill before it was sent to the White House.

On a party-line vote, Republicans shelved the call for an investigation, and Hastert's office did not respond directly to Pelosi's charges.

But other Republicans fired back, accusing her of playing politics. "They're not even in favor of deficit reduction," Rep. Jim Nussle of Iowa said of the Democrats. He said a Senate clerk involved in the controversy should resign "out of honor to the basic tenets of the Constitution" — or be fired.

The political rhetoric aside, the events marked the latest — but not likely the last — development in a controversy with little if any precedent.

Republicans said — and Democrats did not disagree — that the legislation Bush signed correctly reflects the congressional majority's intent on issues of rented medical equipment under Medicare, the section where the bill's text inexplicably appears to have been changed twice.

One lawsuit has been filed challenging the bill's constitutionality.

"The version that was signed into law by the president never passed the U.S. House," says the suit filed by Jim Zeigler, a lawyer in Mobile Ala. An eldercare lawyer, Zeigler said in his suit he does not know whether to advise clients to heed the Medicaid nursing home regulations that had been in effect, or the ones contained in the law Bush signed last week.

Zeigler's claim underscores the sheer breadth of the legislation, which called for dozens of changes in Medicare, Medicaid, student loan and other federal benefit programs as part of an effort to save the government $39 billion over five years.

The legislation itself was the subject of political struggle as it made its way through Congress.

After a year-end weekend of harried closed-door negotiations among GOP leaders, it passed the House last December on a vote of 212-206. It cleared the Senate on the strength of Vice President Dick Cheney's tie-breaking vote, but not until Democrats forced two minor changes that required a revote in the House. The outcome that time was 216-214.

That set the stage for last week's White House signing ceremony.

But not long before Bush was to sign the bill, Hastert and Senate Majority Leader Bill Frist, R-Tenn., were conferring, trying to determine whether the measure was valid.

It turned out that a part of the bill concerning Medicare reimbursement for rented medical equipment had been changed by a Senate clerk.

Aides in both parties say the Senate-passed bill said ownership of certain rented medical equipment should transfer to patients after 13 months, as GOP leaders intended when they put together their final compromise.

But for reasons that remain murky, the formal papers that were carried from the Senate to the House said ownership of the equipment would transfer after 36 months.

The House agreed to the measure, lawmakers evidently thinking they were voting on the 13-month provision. After the vote, a Senate clerk replaced the "36" with a "13" before the bill was sent to the White House.

Concerned, Senate Republicans sought and won agreement from Democrats to pass a follow-up measure affirming that Congress' intent had been to set the rental period at 13 months.

House GOP aides made the same request of Pelosi's staff, but were rebuffed.