The plea-bargain exceptions are:

• When a defendant agrees to provide "substantial assistance" in an investigation. Ashcroft said the message is, "if defendants will cooperate, the green light is on for negotiation."

• Under so-called "fast-track" programs aimed at unclogging court dockets in which certain types of defendants are given a preset charge and sentence lower than that called for under federal guidelines. These programs, which will be reviewed individually by the Justice Department, are popular for common immigration and drug violations in the Southwest.

• When prosecutors decided that the original charges will be tough to prove in court because of witness access problems, suppressed evidence or some other reason.

• If the possible sentence would be unaffected by a charge under a lesser offense.

• When "enhancements" that could result in a longer sentence, such as a defendant facing multiple charges connected with the main crime, remove any incentive for the defendant to plead guilty. Enhancements for firearms offenses, however, would generally have to be included.

• On a case-by-case basis for other reasons with written approval by a supervisor.