Chicago Bears quarterback Jim Miller had his 1999 season ended prematurely yesterday when he was suspended for four games by the NFL for violating the league's drug policy on steroids. Miller said he unknowingly ingested a banned substance that was contained in an over-the-counter nutritional supplement.

"I made a dumb mistake," Miller said during a news conference at the Bears' training facility in Lake Forest, Ill. "By no means was this done knowingly. I would never take steroids. You guys [in the media] have seen my physique. This was an honest mistake."

Miller said he took a supplement he declined to name that was purchased at a local store. He said he had run out of his usual supplement and was waiting for it to go on sale when he used another product for four days last September.

He described it as a dietary supplement that he used to enhance his workouts, just as he said many of his teammates and players around the NFL do all the time. His mistake, he added, was not reading the ingredients on the bottle, one of which contained a trace amount of the anabolic steroid nandrolene.

"No way it was done knowingly," he said. "Anyone who knows me knows I would never take steroids as a quarterback."

Miller took a random drug test on Oct. 4 and was informed by mail on Nov. 10 that he had failed it. League policy calls for a second test to be taken, but Miller and his agent, Joe Linta, said a trace amount was found in the second test, as well.

Linta said he and Miller had been told by league and team officials there was a good chance the second test could have been steroid free. If he had declined to take Part B of the test, he would have been suspended immediately. Linta said he was informed that Miller failed the test on Monday night.

Miller is the third player in the last two weeks to face an automatic four-game suspension for steroid use. Giants rookie safety Lyle West and Jets tackle Jason Ferguson also were suspended. No fines were assessed, but Miller will lose four game checks--a total of about $100,000.

The Bears are 5-7 and Miller, 28, has been the starter for the last three games, revitalizing the offense by averaging 327 passing yards a game. In a 27-24 overtime loss to Minnesota, Miller completed 34 of 48 passes for 422 yards and three touchdowns, the best day by a Chicago quarterback in more than 30 years.

The Bears will now start Shane Matthews Sunday at home against Green Bay, with rookie first-round draft choice Cade McNown the back-up and recently signed Craig Erickson the emergency quarterback.

Miller had originally gotten his chance to start because of injuries to both Matthews and McNown, and made the most of the opportunity. He's also played for Pittsburgh, Atlanta and Jacksonville before the Bears signed him as a free agent this season.

Mark Hatley, the Bears vice president of player personnel, said Miller is still in the team's plans for next season, though he does become a free agent at the end of the '99 season.

"I can't explain how disappointing this is,'" Miller said. "Our team has done very well. Out of all the people to let down the team, I thought I'd be the last to do it. . . . The toughest thing I've had to do was to come in and tell my teammates what happened."