WASHINGTON, Nov. 28 — Lobbyists for Eli Lilly & Company, the pharmaceutical giant, did not have much luck when they made the rounds on Capitol Hill earlier this year, seeking protection from lawsuits over a preservative in vaccines. Senator Bill Frist, Republican of Tennessee, tucked a provision into a bill that went nowhere. When lawmakers rebuffed a request to slip language into domestic security legislation, a Lilly spokesman said, the company gave up.

Now, in a Washington whodunit worthy of Agatha Christie, the provision has been resurrected and become law, as part of the domestic security legislation signed on Monday by President Bush. Yet in a city where politicians have perfected the art of claiming credit for deeds large and small, not a single member of Congress — or the Bush administration — will admit to being the author of the Lilly rider.

"It's turning into one of Washington's most interesting parlor games," said Dave Lemmon, spokesman for Senator Debbie Stabenow, Democrat of Michigan, who has promised to introduce legislation to repeal the provision. "There's a lot of guessing, a lot of speculation as to who did this."

The provision forces lawsuits over the preservative, developed by Eli Lilly and called thimerosal, into a special "vaccine court." It may result in the dismissal of thousands of cases filed by parents who contend that mercury in thimerosal has poisoned their children, causing autism and other neurological ailments. Among them are Joseph and Theresa Counter of Plano, Tex., devoted Republicans whose party allegiance has run smack into family ties.

The Counters' 6-year-old son, Joseph Alexander, was normal and healthy until he was 2, they say. Then he took an unexplained downward slide. Today, the boy struggles with words. He cannot zip his pants, snap buttons or tie his shoes. His parents say tests eventually showed that he had mercury poisoning, which they attribute to vaccines. They sued last year.

"I know that our legislative system can be very, very messy at times," said Mr. Counter, a political consultant, who with his wife has spent many thousands of dollars on medical care and therapy for their son. "But for them to attempt this, in the dead of night? It disgusts me. This morning, I am ashamed to be a Republican."

With lawmakers now scattered across the country, Washington is rife with speculation about who is responsible for aiding Lilly, a major Republican donor. During the 2002 election cycle, the company gave more money to political candidates, $1.6 million, than any other pharmaceutical company, with 79 percent of it going to Republicans, according to the Center for Responsive Politics, a nonprofit research group that monitors campaign finances.

Critics of the provision, mainly Democrats and trial lawyers, are quick to point out that the White House has close ties to Lilly. The first president Bush sat on the Lilly board in the late 1970's. The White House budget director, Mitchell E. Daniels Jr., is a former Lilly executive. The company's chairman and chief executive, Sidney Taurel, was appointed in June by President Bush to serve on a presidential council that will advise Mr. Bush on domestic security.

The White House, however, has said that it did not ask Congress for the provision. Rob Smith, a spokesman for Lilly, said that the company's lobbyists "made absolutely no contact with Mitch or anyone in his office about this," and that Mr. Taurel "did not at any time ask" for any favors.

"It's a mystery to us how it got in there," Mr. Smith said of the provision.

Senator Frist has said it is a mystery to him as well. As the Senate's only doctor, he sought to include the provision in legislation that would promote the availability of vaccines. But the vaccine bill is stalled; Senator Edward M. Kennedy, the Massachusetts Democrat who is chairman of the Senate health committee, opposes it. Mr. Frist's spokesman said he did not seek to have the provision included in the domestic security bill.

On Capitol Hill, Congressional aides-turned-detectives have traced the emergence of the provision to the Veterans Day weekend. Flush from their party's victories on Election Day, and with a mandate from President Bush to pass a domestic security bill, Republican negotiators in the House and Senate holed up for three days in the Capitol to hammer out the details, said Richard Diamond, spokesman for the retiring House majority leader, Representative Dick Armey of Texas.

One aide said the language mysteriously appeared in the House version of the bill in entirely different type than the rest of the measure, as though someone had clipped it out of Mr. Frist's legislation and simply pasted it in. Mr. Diamond said all the negotiators supported the move, but would not say who was responsible.

"If you want to give somebody credit for it," he said, "Mr. Armey takes ultimate credit. It's his bill. We are happy to wrap ourselves around it, but Mr. Armey is not a doctor, like Senator Frist. He's the source of the language."

Whether thimerosal is truly harmful is the subject of intense scientific controversy. Earlier this year, the National Academy of Sciences issued a report saying there was no scientific evidence either to prove or disprove a link between thimerosal and brain disorders like autism. But the academy did find that such a link was "biologically plausible," and so it urged pharmaceutical companies to eliminate thimerosal, which has already been removed from many vaccines, as quickly as possible.

The Lilly rider closes a loophole in a 1986 law that requires victims to file claims with the vaccine court, which awards payments from a taxpayer-financed compensation fund, before going to civil court. But the law covered only vaccines themselves, not their ingredients, which meant people like the Counters could sue ingredient manufacturers like Lilly directly.

While Washington debates the origins of the provision, families are fuming. Some say the government fund will do them no good, because they have missed the statute of limitations — three years from the date symptoms first appear — for filing claims. Scott and Laura Bono of Durham, N.C., say that while their son Jackson, now 13, showed symptoms similar to autism six or seven years ago, it was not until August 2000 that they learned he had mercury poisoning. They filed suit just the other day.

Aware of the controversy, lawmakers in both parties have pledged to alter the thimerosal rider, but are arguing about how to do so. While many Democrats want it repealed, Republicans have suggested that they may simply alter the language to apply to future cases only.

"I'll believe it when I see it," said Mr. Waters, the Counters' lawyer.

In the meantime, Mr. Smith, the Lilly spokesman, said his company would soon go to court to seek dismissal of the suits.

That news made Theresa Counter cry.

"It just makes me sick," she said. "I cannot tell you how devastating it is to think that we might have to start all over."

Copyright The New York Times Company

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