Three U.S. senators are calling for an official review of the Chesapeake Bay restoration effort after news reports that the government agency leading the cleanup has overstated its progress.

Sens. Barbara A. Mikulski (D-Md.), Paul S. Sarbanes (D-Md.) and John W. Warner (R-Va.) sent a letter to the Government Accountability Office asking for it to assess the Chesapeake Bay Program's reported progress toward bay restoration.

"Questions remain about whether the information currently reported by the Bay Program provides an accurate depiction of Bay conditions and the amount of progress made toward restoration goals," according to the lawmakers' letter, dated Friday.

A House committee is planning to review the bay restoration efforts.

The Chesapeake Bay Program, the federal and state partnership directing the restoration of North America's largest estuary, has used numbers from a computer model to report significant reductions in the amounts of phosphorus and nitrogen running into bay waters.

The Washington Post reported last month that the model was twice found to have rested on erroneous assumptions that overstated the results of the cleanup. Some scientists questioned whether the model should have been used as the primary measure of progress, particularly when actual water monitoring tests appeared to differ, showing little or no progress.

The Chesapeake Bay Program and outside scientists have split on the reporting of the amount of oxygen-depleted water in the bay, considered a key indicator of bay health. The Chesapeake Bay Program reports "indications of an improving trend since 1985." Other scientists report no trend.

Bay program officials say that they have been using the best available science and that their models have been improving.

"The Chesapeake Bay Program welcomes the call of the senators for a review of the program," Rebecca Hanmer, director of the Chesapeake Bay Program office, said in a statement. "We also know that we must constantly evaluate our assessment methods and strive for further improvements . . . The program has a strong history of putting all of our work out for public scrutiny, and we take great pride in the scientific integrity of our work."

A spokesman for the GAO said the request from the senators is under review.

Other lawmakers will consider the issues Aug. 20, when the House Committee on Government Reform will meet in Hampton, Va., to consider how to evaluate the differing assessments of bay health.

"If there's conflicting data, how do we know what cleanup efforts have been working and what to do in the future?" said Tom Gordy, chief of staff for Rep. Edward L. Schrock (R-Va.), a member of the committee.