The Federal Communications Commission has determined this week that singer Janet Jackson's brief breast-baring incident during CBS's broadcast of the Super Bowl halftime show in February was indecent and has proposed fining 20 CBS-owned stations a total of $550,000, according to FCC sources.

If approved, it would be the largest indecency fine ever levied against a television broadcaster.

The show also featured a crotch-grabbing rapper and several S&M-clad dancers gyrating behind Jackson and fellow pop star Justin Timberlake. Toward the end of the routine, Timberlake ripped off part of Jackson's leather bodice, exposing her breast for a few seconds. "A wardrobe malfunction," Timberlake said later.

FCC Chairman Michael K. Powell took the unusual step of personally launching an indecency investigation on the Monday after the Super Bowl, which was seen by about 90 million viewers. The FCC's enforcement bureau took up the case and concluded the investigation faster than usual.

The bureau has ruled that the halftime show violated the agency's indecency standards, which say that sexual or scatological material may not be broadcast over the airwaves between 6 a.m. and 10 p.m., when children are most likely to be watching.

The finding led to Powell's office placing an order before the five FCC commissioners, assessing the 20 CBS-owned stations the maximum fine of $27,500 each. If three of the five commissioners approve the order, parent company Viacom Inc. would be liable for the fine. It would be only the third fine levied against a television broadcaster in FCC history and is by far the largest. The agency has fined numerous radio broadcasters over the years for millions. It recently proposed fining Viacom's radio unit, Infinity Broadcasting, about $400,000 for remarks by shock jock Howard Stern and others.

The FCC would not comment yesterday.

Viacom owns 20 CBS and 19 UPN stations. CBS programming, however, is seen on more than 200 affiliate stations, including Washington's WUSA, Channel 9. The FCC chose not to fine the affiliates, saying they had no control over the production of the halftime show and no knowledge it would contain the racy material, said FCC sources, who would not comment on the record on a pending proceeding. The halftime show was produced by another Viacom subsidiary, MTV, known for its sexually suggestive videos and original series.

"We have received no notification [of the potential fines] and therefore we decline to comment," CBS spokesman Gil Schwartz said. "I will note that Viacom did report back to the FCC several months ago after concluding an extensive investigation that concluded that no one from CBS or MTV or Viacom had any prior knowledge of what Jackson or Justin were planning to do. And we also have expressed regret numerous times."

The Super Bowl incident was the best known of a number of offensive radio and TV broadcasts over the past two years that have spurred outrage from viewers and action from lawmakers.

Within months of the Super Bowl broadcast, the House and a Senate committee each approved bills that would give the FCC the authority to increase its maximum fine for indecency violations from $27,500 to $275,000 in the Senate bill and $500,000 in the House version. Both bills have languished, but an amendment increasing the fines recently was attached to a Defense Department authorization that has passed both houses. (The FCC recently voted to increase its maximum fine from $27,500 to $32,500 to keep up with inflation, as it is required to do, but the increase has not gone into effect.)

The FCC also has begun fining stations for each utterance of indecent material. For example, in the past, if a radio show contained three indecent utterances, the show would receive one fine. Now, the show would likely receive three fines. Broadcasters could face multimillion-dollar daily fines if the proposed FCC fine increases become law.

In April, the FCC fined six Clear Channel Communications Inc. stations for three utterances by Howard Stern that were ruled indecent, a total of 18 fines. Clear Channel has since paid the FCC $1.75 million to clear all indecency fines and pending investigations. Citing a zero-tolerance policy toward indecency, Clear Channel in February pulled Stern from all six of its stations that carried him. Yesterday, Infinity and One Twelve, a company co-owned by Infinity and Stern, filed a $10 million lawsuit against Clear Channel for the incident, saying the radio giant had dropped the Stern show improperly and owed the company license fees.

"Howard Stern is the only one who's broken the law," Clear Channel spokesman Andrew W. Levin said in a statement. "His contract explicitly requires his show comply with all FCC rules and regulations. On several occasions, it clearly did not. Clear Channel Radio had both a legal right and an obligation to stop broadcasting it."

Both the House and Senate versions of the indecency bill contain language that would allow the FCC to fine individual performers, which performers' unions have opposed. If such fines become law, Stern said he would play out the final 18 months of his contract with Infinity and quit, possibly to join one of the two satellite radio companies, XM or Sirius, neither of which is subject to FCC decency standards.

FCC Commissioners Michael J. Copps, a Democrat, and Kevin J. Martin, a Republican, have pushed hardest for tougher indecency punishments. with Copps dissenting from some recent fines, saying they didn't go far enough. For instance, Copps opposed an April fine against a Clear Channel subsidiary, saying the stations should have been subject to broadcast license-revocation hearings.

The FCC's enforcement bureau may be close to a ruling on a December 2003 incident in which actress Nicole Richie uttered two obscenities on live television during a Fox broadcast of the Billboard Music Awards show.

Justin Timberlake pulls off part of Janet Jackson's costume to expose her breast during their Feb. 1 performance at the Super Bowl halftime show.