WASHINGTON – Rules to reduce conflicts of interest at the National Institutes of Health went too far, the agency says, so it’s easing a prohibition on owning stock in drug and biotechnology companies.

Under the new regulation, some 200 senior employees as well as their spouses and minor children may own no more than $15,000 worth of such stock. Any holdings above that amount will have to be sold by January 30.

An interim rule issued in February would have had a much broader impact. Under that rule, about 6,000 scientists and other high-ranking employees would have been required to sell their stock holdings in such companies entirely. An additional 12,000 employees would have been required to keep such holdings to a maximum of $15,000 in value.

The divestiture rule proved unpopular with NIH employees and threatened the agency’s ability to attract top talent, NIH officials had said prior to yesterday’s announcement. It never went into effect. The revisions take effect next Tuesday.

While the stock ownership rule was relaxed, a ban on consulting work in industry remains in place.

The agency issued the new ethics rules for its employees after press reports that some researchers received thousands of dollars from outside industries that had the potential to influence their work at NIH, the primary federal agency for medical research.

“The issues that we were facing were not related to stock holdings in great part,” said NIH Director Elias Zerhouni. “Therefore, this is where I convinced myself it was not necessary to have a blanket divestiture rule.”

Mr. Zerhouni said he decided to continue to keep in place a ban on outside consulting work by NIH staff for pharmaceutical and biotechnology companies, as well as companies that make medical devices.

“These rules are the most restrictive of any rules we know about in the world of biomedical research,” Mr. Zerhouni said. “The rules as you see them today are extremely stringent. With the ban on consulting for paid activities, I think Congress should be very fully reassured we’ve addressed the fundamental issue of public trust in the integrity of the science.”

While the limit on stock holdings focuses on senior employees, Mr. Zerhouni said that other employees will have their investments reviewed on a case-by-case basis when they file their financial disclosure reports. In some cases, those employees could be directed to sell their holdings if supervisors believe a conflict of interest exists.

A recent internal review at NIH showed that 44 scientists violated one or more NIH rules: Those rules required them to report outside income on financial disclosure forms, take personal leave to do private work and seek prior approval for the arrangements.

Thirty-six of the scientists are still employed at NIH and have been referred for possible disciplinary action. Nine of those 36 have also been referred to the Health and Human Services Office of Inspector General for investigation of possible criminal violations.

Response from Capitol Hill to the revisions was positive.

“It’s important that the American people have full confidence in the National Institutes of Health,” said Rep. Joe Barton, a Republican of Texas and chairman of the House Energy and Commerce Committee. “Dr. Zerhouni has done an admirable job addressing a difficult, yet critical, issue.”

“It is essential for NIH to meet stringent ethical standards, while allowing the exchange of ideas and information that is the lifeblood of scientific discovery,” said Senator Kennedy, a Democrat of Massachusetts. “The new regulations strike that balance effectively. They guard against improper conflicts of interest, and will allow NIH to continue to attract researchers of the highest caliber.”