Last fall, on the final weekend of the National Football League's regular season, an official in the Los Angeles Coliseum awarded the Raiders a touchdown when they legally did not score one.

Fans watching instant replays in their living rooms knew it. Patrons watching big screens in bars knew it.

But the officials didn't.

When Los Angeles wide receiver Dokie Williams caught a pass in the end zone, put one foot down within bounds, and his other foot down out of bounds by about a yard, the official should have called an incompletion. NFL rules say a receiver has to have both feet within bounds for a pass to be a completion.

The call's significance in the game was minor. It gave the Raiders their only touchdown in a 13-7 loss to Pittsburgh.

Three months later, it became much more important. This week, the call gave the NFL the nudge it needed to approve the instant replay for nine nationally televised preseason games this summer, beginning with the Hall of Fame Game in Canton, Ohio, between the New York Giants and the Houston Oilers.

If the experiment works well, there is a "50-50" chance the replay will become part of NFL games in 1986, said Tex Schramm of the Dallas Cowboys, chairman of the league's competition committee, which proposed the replay.

"We want to correct the obvious wrong call," said Miami Dolphins Coach Don Shula, a member of the committee. "We want to change the call where there are no ifs, ands and buts about it -- it obviously was missed. We just want to see what everybody sees at home. The best example is the Raiders-Steelers call."

Thursday, during the NFL's annual winter meetings at the Arizona Biltmore Hotel, 23 of the 28 teams approved the instant-replay experiment, which perhaps more accurately should be called a "monitoring system" of the network telecast.

This is how it works:

The league will station a "replay official" in front of a TV monitor in a private box somewhere in the stadium. The official, who probably will be chosen from a pool of officials otherwise not assigned to work that day, will watch the same game everyone else is watching.

If and when he sees an obviously questionable call -- what the new rule says "when viewed live clearly indicates that a mistake may have been made" -- he will call down to the field on a radio connected to one of the officials to tell them he wants to watch a replay. (The officials also may call the replay official if they feel a replay may be needed.)

Then, the officials will meet on the field and wait to hear from the replay official, just as with any controversial call.

In fact, it's likely fans in the stands and those watching on TV will have no idea that the replay rule has been invoked.

"That's the intent," Shula said. "It shouldn't be a big deal."

While the officials confer on the field, their man in the box will sit in front of his TV. And wait.

The next step is up to the network televising the game. If the replay pops onto the screen in 20 seconds, the replay official will watch it and act accordingly.

The rule says that if the replay confirms a mistake, "the call would be reversed unless another ruling supersedes." If, for example, the call in question concerns a fumble, the replay official's ruling would not matter if the officials on the field called the player already down.

The replay official cannot call penalties, or look at action on another part of the field during the play in question.

"We're not looking for things," said Val Pinchbeck, the NFL's director of broadcasting.

If the replay doesn't come on in 20 seconds, play continues as if nothing had happened.

The NFL cannot ask the network for a special replay. In fact, there will never be any communication between the officials and the networks.

"We will have nothing to do with it," said Ted Nathanson, NBC's coordinating producer for football. "The networks don't want to become involved in the rules of the game. That would just be chaos."

Common sense dictates that the replay official will get what he wants to see, anyway.

"If it's a controversial call of any kind, we'll replay it within 20 seconds," Nathanson said.

The reason the NFL put a time limit on the rule is simple. During a week in which the league passed numerous rules and procedures to shorten the length of games (now an average of 3 hours 9 minutes), it doesn't want to add ponderous minutes for replays.

Controversial calls already produce conferences of officials on the field, the competition committee figured. The addition of a replay official won't add to the length of the conferences, and could even shorten them.

The NFL denies it is following the lead of the U.S. Football League, which allows replays in several specific ball-possession situations. The two systems are very different; the USFL allows "challenges" from coaches, indicated when an official tosses a red flag onto the field.

The NFL will allow no challenges and no red flags. It also will not limit itself to what can be replayed, as the USFL has.

"You'd hate to tie yourself down," said Schramm.

The only similarity between the league's rules is the reliance on the network feed for the replay, with no communication between the replay official and the network's truck outside the stadium.

NFL officials say it's likely the replays will be rarely used during the preseason games.

One league official wondered if there will be any at all.

Yet the replay, strongly backed by the Washington Redskins, ran into its share of criticism. The New York Giants, New York Jets, Houston Oilers, Kansas City Chiefs and Los Angeles Raiders voted against the plan.

Raiders executive assistant Al LoCasale said his records showed the Raiders voted for the replay, but confirmed that the team did have reservations about it.

"We would rather that the network feed not be involved," LoCasale said. "If we get the right replay, that's fine. But if we don't . . . "

In 1978, the NFL conducted an in-depth study of the instant replay, studying how long it would take to run replays from different angles on controversial plays.

It took too long, Pinchbeck said, and that was that.

This time, relying on just one replay coming 20 seconds following the play, it may work.

"If one bad call that costs somebody a game is changed," Shula said, "then it's worth the experiment."

Just two days after they were tabled by the National Football League, helmet radios are back.

On the final day of the league's winter meetings, the 28 teams unanimously approved a plan to allow eight teams to experiment with tiny voice transmitters and receivers during the 1985 preseason.

The Seattle Seahawks and San Francisco 49ers will be two of the teams to use the radios. Six others will be chosen before the preseason. Each team will use the radios for only one game.

The plan, which was tabled earlier in the week, was approved today when the competition committee found a way to turn the quarterback's transmitter on right before the snap and off immediately after it, so it would not be misused during a play.

The transmitters and receivers are designed to allow offenses to hear the quarterback's signals in noisy stadiums.