Proposed rules to help the FBI catch terrorists could lead to innocent Americans being spied upon by government agents or informants "all without any basis for suspicion," a group of Democratic senators said Wednesday.

The rules, known as the attorney general guidelines, have not been approved or even publicly released yet, but four Democrats joined a growing chorus of lawmakers raising concerns after being briefed on what the guidelines say.

Among their fears: Americans could be targeted in part based on their race, ethnicity or religion — or free speech activities protected by the Constitution.

"As you know, attorney general guidelines were first implemented in the wake of the FBI abuses of the 1960s and 1970s, and serve as one of the most important bulwarks against future abuses," the senators said in a letter to Attorney General Michael Mukasey.

The four Democrats — Sens. Dick Durbin of Illinois, Russ Feingold of Wisconsin, Edward M. Kennedy of Massachusetts and Sheldon Whitehouse of Rhode Island — indicated they remained concerned even after reassurances from officials during the Justice Department briefings.

The lawmakers asked Mukasey to hold off finalizing the rules to allow a public review.

"Given the importance of these guidelines, providing a period of time for public comment would be a reasonable and responsible way to move forward and achieve the best possible end result," the Democrats wrote.