UPDATE 1-Eight senators back Whole Foods in fight with FTC

(Adding that subcommittee chairman did not sign, paragraph 5)

WASHINGTON, Dec 15 (Reuters) - The Federal Trade Commission acted hastily in changing its rules for investigating mergers and the changes made the assessment process less fair, eight senators said in a letter sent to the commission.

The rules have come under sharp criticism from Whole Foods WFMI.O, which has been battling the FTC since February 2007 over whether it should be allowed to merge with rival Wild Oats. The merger was completed in August 2007 but the FTC is still assessing it, and could order it undone.

In a letter dated Dec. 12, the senators criticized the FTC for accepting public comments for just 30 days on proposals to speed up the agency’s process for assessing mergers and having commissioners preside over hearings held prior to internal trials by FTC administrative law judges. Commissioners also vote to investigate mergers.

“Regardless of whether the procedure and substance of the changes technically comply with the statutes governing FTC rule-making, we are concerned that they may fall short of the standard of prudence with which the FTC ought to wield its considerable power,” said the letter which was signed by Sen. Patrick Leahy, the Vermont Democrat who chairs the Senate Judiciary Committee, and Arlen Specter of Pennsylvania, the ranking Republican on the panel.

Antitrust subcommittee chairman, Democratic Sen. Herb Kohl of Wisconsin, did not sign the letter.

The other signatories were Democratic senators Tom Harkin of Iowa, Dianne Feinstein of California, Charles Schumer of New York, Bill Nelson of Nebraska and Benjamin Cardin of Maryland as well as Sen. John Cornyn, a Texas Republican.

“Obviously we take all letters from Congress seriously,” said FTC spokesman Mitch Katz, who declined to comment on the substance of the letter. (Reporting by Diane Bartz; Editing by Phil Berlowitz and Tim Dobbyn)