WASHINGTON, March 21 — Expert advisers to the government who receive money from a drug or device maker would be barred for the first time from voting on whether to approve that company’s products under new rules announced Wednesday for the F.D.A.’s powerful advisory committees.

Indeed, such doctors who receive more than $50,000 from a company or a competitor whose product is being discussed would no longer be allowed to serve on the committees, though those who receive less than that amount in the prior year can join a committee and participate in its discussions.

A “significant number” of the agency’s present advisers would be affected by the new policy, said the F.D.A. acting deputy commissioner, Randall W. Lutter, though he would not say how many. The rules are among the first major changes made by Dr. Andrew C. von Eschenbach since he was confirmed as commissioner of food and drugs late last year.

Advisory boards recommend drugs for approval and, in rare cases, removal, and their votes can have enormous influence on drug company fortunes.

“The $50,000 threshold is something that we think strikes an appropriate balance between” getting smart advisers and reassuring the public that their advice is not tainted, Dr. Lutter said.

The changes are intended to respond to a growing chorus of critics who contend that drug and device makers have hijacked the Food and Drug Administration’s approval process by paying those who serve on the agency’s advisory panels.

In one famous example, 10 of the 32 advisers who voted in 2005 to allow the painkiller Bextra to remain on the market and the painkiller Vioxx to return to the market despite safety worries had taken money from the drug makers. Under the new rules, their votes would not have counted and the committee would have voted to keep both drugs off the market.

In the end, the F.D.A. removed Bextra from the market anyway, and Vioxx has never returned. But the controversy surrounding that panel’s vote, and similar ones, tarnished the process and provided new fodder for critics in Congress.

Representative Maurice D. Hinchey, Democrat of New York, said he was delighted with the change, which will not become final until the end of a 60-day comment period.

“So many lives have been lost as a result of the failure of the F.D.A. to review drugs properly,” said Mr. Hinchey, who for two years has proposed legislation to ban agency advisers from having financial conflicts of interest. “The F.D.A. is now moving back to where it was supposed to be, a principled agency that protects the people.”

But Representative Rosa DeLauro, Democrat of Connecticut and chairwoman of a subcommittee that has oversight over the F.D.A. budget, said there might be undisclosed loopholes that make the new rules toothless. “I am skeptical, given their recent track record of putting political and corporate interests above science,” Ms. DeLauro said.

With the change in the leadership of Congress, Mr. Hinchey’s legislation had better prospects of passage. Daniel E. Troy, a former F.D.A. general counsel, said the new rules were an effort to pre-empt the Hinchey bill.

“F.D.A. is trying to strike a balance here,” Mr. Troy said, “and they would rather strike it themselves than have it struck for them.”

Drug makers routinely hire doctors as consultants for marketing and research. The New York Times reported on Wednesday that records in Minnesota show that at least 20 percent of licensed physicians in the state received money from drug makers between 1997 and 2005 — an average of $10,000.

While there were some conflicts under the old rules that led to outright exclusions, like a prohibition on advisers holding $100,000 or more in stock in the company at issue, the agency could waive almost any other financial conflict, including tens of thousands of dollars in income.

The announcement of waivers was becoming so common at the start of advisory committee meetings that they took on the feel of fast-talking car commercials, but because of confidentiality rules, the conflicts underlying the waivers were generally not disclosed. The public did not know whether the conflicted experts got $10 or $10,000.

The agency has long defended its process of selecting expert advisers, and some in the agency’s drug center opposed in internal deliberations strict rules that would have prevented them from picking the experts they wanted.

Waivers to that rule are still possible under the present system, but only the commissioner can approve them, something Mr. Lutter said would probably be rare.

Some conservatives were not happy with the new rule.

“There are going to be more good people who can’t get over the hurdles, and I don’t think that’s a good thing,” said Jack Calfee, a resident scholar at the American Enterprise Institute. But Dr. Peter Lurie of Public Citizen, an advocacy group often critical of the F.D.A., praised the new rules.

“I think it’s likely to improve the quality of the recommendations, remove the taint of the recommendations and improve the credibility of the recommendations,” Dr. Lurie said.

The Pharmaceutical Research and Manufacturers of America said it was still studying the new rules.

Advisory panels are important to the F.D.A. not so much because they provide the agency with expert advice — the F.D.A. can get that privately any time — but because they serve to increase public confidence in the agency’s decisions.

F.D.A. officials have long said that such panels help the public better understand the many factors it must weigh in its decisions. Advisory panels are a crucial means by which the agency pulls back the curtain on its decision-making, so declining confidence in the panels seriously undercuts their utility to the agency.

Although the new rules would most likely lead some of the agency’s present advisers to drop off their committees, many advisers are likely to welcome the greater clarity that the new rules bring. Under the old system, committee members rarely knew what kind of conflicts would lead to problems.