Here's an idea for John Riggins.

Tell the Michigan Panthers he's interested.

Sure.

Tell them it's been his lifelong dream to play in the United States Football League.

"I know that sounds funny, because the league is only 6 months old," Riggins should tell them. "But ever since I was a little boy in Kansas, I knew there would be a USFL. Yes, sir. I want to end my career as a Panther beating my head out for two yards a crack in places such as Birmingham."

He should look sincere saying that.

Then Riggins should say, "It'll cost you $2 million."

When the boss Panther says, "We can handle that," Riggins should add, "That's cash today. That's for me. Two years max. Now, let's talk about the Hogs."

"We don't want any Hogs," the boss Panther says.

"The $2 million's for me, and you mail $4 million to Washington to be split up among the Hogs, and we sign a deal saying you triple the salary of any Hog who wants to come here anytime."

"John, come on."

"Now, let's talk about the Fun Bunch . . ."

This would be John Riggins' way of telling the boss Panther to not let the door hit him on the way out. He is, this would say, happy with the Redskins and those Hogs who have made his life a dance in top hat and tails. By showing the boss Panther to the door (perhaps handing him a beer for the road), Riggins would say it's ludicrous to expect the Super Bowl's most valuable player to leave a championship team likely to give him a million-dollar contract itself.

But.

You can get a charley horse in your brain trying to predict Riggins' behavior. A rule of journalism: never guess the next move of a guy who once cut his hair in a Mohawk. Only three summers ago, Riggins walked out in the middle of a $1.83 million, six-year contract with the Redskins.

Who knows? Instead of keeping a date with NFL Films yesterday at Redskin Park, Riggins showed up at an Alexandria fire marshal's shindig. Bobby Beathard, the Redskins' general manager, would like to call Riggins--but Riggins has changed his phone number and, one assumes, given it only to certified Hogs.

No one knows what Riggins might do, because, first of all, no one knows what the Panthers are up to.

Are they serious?

Their season opener is only two weeks away.

The Super Bowl was three weeks ago.

Yet the Panthers' vice president, Shire Rothbart, said yesterday his team had not talked to Riggins.

"We are certainly interested," Rothbart said, "but the first step is to find out if Riggins is interested."

But David Remnick of The Post reported two days ago that the Panthers already had offered Riggins $1 million for two seasons.

"It is a constant source of amazement to me where you newspaper people get your figures from," Rothbart said. "Particularly in this case, because I haven't got around to any figures myself."

An old state editor once said, "Kid, don't believe anything you hear and only half of what you see." What we're hearing from Michigan is the mysterious sound of someone blowing smoke in our ears, trying to sell tickets in a town where everybody's out of work.

But let's suppose, as Rothbart said, "Every USFL team certainly decided they needed a superstar for credibility," and Riggins is the Panthers' chosen one.

So what would the Panthers offer Riggins?

Three factors enter the equation here: 1) the Panthers play in the Silverdome, with 80,000 seats; 2) the owner, Alfred Taubman, is (according to Forbes magazine) the wealthiest man in a state with people named Ford, and 3) Riggins has a career-long preoccupation with long-term financial security in case of injury.

Let's suppose, then, that the Panthers have no money problems and can offer Riggins a contract worth more than the reported offer to Anthony Carter. Carter's deal is between $325,000 and $525,000 a year. Let's suppose that puts Riggins in the $600,000 range for two seasons. That is a lot of money for a 33-year-old running back who had his greatest season, not coincidentally, when his offensive line had one of the NFL's all-time great seasons. A veteran football observer said, "If Riggins goes to the USFL, I predict he will lead the world in two-yard gains."

Do you pay $600,000 for a 12th-year runner who may or may not be wonderful without the Hogs? A season before, Riggins was respectable but put no one in mind of Larry Csonka.

What Riggins will figure out (yes, a prediction anyway) is that he is worth more to the Redskins than the Panthers. He'll get his fair raise from his $330,000 contract, with incentives that might take it to--where? --maybe $600,000 a year.

"There is no sense of urgency whatsoever," said Redskins owner Jack Kent Cooke, slyly dismissing the Panthers as a threat. "I expect to meet with John before this week is over, and we fully expect to come to terms."

As for the Panthers' owner, Rothbart said Alfred Taubman is on a cruise up the Nile River.

That's in Egypt, where there is no USFL team, which is really too bad because the Pharoahs would be a good nickname and the team mascot could be an asp.

Maybe they could announce they're offering King Tut a big deal to come out of retirement.