The 10th season of Playing Football begins with a guarantee. If, as Super Bowl XVIII nears, this column is showing a sizable profit, there will be no imaginary megabucks wagered on the final weeks' predictions. The reason follows:

Eight years ago, after the NFL's third-week games of Oct. 4, I was feeling unbeatable. I had picked Dallas, giving 6 points at Detroit, for $1,000; San Francisco, even, at Kansas City for $1,000, and Buffalo, giving 6 at home against Denver, for $2,000. All three selections won, enabling the column to quickly overcome a $2,800 loss the first two weekends.

I couldn't help wonder, at that point, how I could be so brilliant at covering the spread while so many other people were struggling. Finally, a friend of a friend of mine couldn't stand my prattling anymore. He already was down $5,000, early in '75, and he was looking for an egomaniacal pigeon to bail him out--and my nose does resemble a pigeon's.

When the friend of the friend said, "Okay, smart guy, if you're so confident this is an easy game, you're never going to have a losing season, right?"

"You're probably right," I replied.

"Okay," he said, "I'll offer you one heck of a price on your going 10 straight years without losing."

"Tell me about it," I shot back.

The price he quoted wasn't the biggest bargain I had ever heard. But the trap was set. Peer pressure, they call it. One of my closest acquaintances had overheard the challenge. It was speak up or shut up. Like a fool, I took the bet.

Now, through nine seasons, Playing Football is plus $31,854, including the vigorish. The won-lost record is 325-274, for 54.2 percent. Last year was a good one, despite the strike: 20 wins, 12 losses, a net profit of $1,950.

But that followed two seasons in which I was life and death to keep from losing my 10-year side bet. The profit in 1980 was $625; in 1981, $250.

So here we go again. The minimum risk is $250 per game; the maximum, $3,000. All imaginary, of course. It's a 20-week endurance test. The line is that published Wednesday morning. Yes, there often are slight but critical changes between those numbers and the ones at kickoff time. I can't help that. It works both ways. It only seems as though it works to your disadvantage all the time.

The opening number has San Francisco 3 1/2 over Philadelphia Saturday. Sunday's card lists Chicago 1 over Atlanta, Tampa Bay 3 over Detroit, Green Bay 4 1/2 at Houston, New York Giants 4 over Los Angeles Rams, Cleveland 1 1/2 over Minnesota, New Orleans 2 1/2 over St. Louis, New England 5 1/2 over Baltimore, Miami 4 at Buffalo, Cincinnati 2 over Los Angeles Raiders, Pittsburgh 7 over Denver (where is the John Elway money?), Kansas City 2 over Seattle and San Diego 3 1/2 over New York Jets. Monday night, in RFK Stadium, Dallas is 2 over Washington.

I will start out conservatively, as usual, risking $250 each on New Orleans giving 2 1/2, Dallas giving 2, Miami giving 4 and Cincinnati giving 2.

The Saints came a long way in a hurry last season under Bum Phillips, although their 4-5 record might not reflect the fact. They should win the NFC West, which isn't saying much. At 75 to 1 in the Super Bowl future book, I couldn't resist them, although Seattle was even more inviting at 100 to 1.

Chuck Knox left Buffalo for Seattle, which explains why I am suddenly so high on the Seahawks and bearish on Buffalo. The Bills were impossible to bet against at home during the early part of a season under Knox. With Knox gone, and Miami opening at Buffalo, the impossible becomes possible. The Dolphins are primed for a fast start, even though David Woodley is still the quarterback.

Dallas-Washington is the game of the week. Both teams will make the playoffs. I'm not sure the Cowboys will be ahead of the Redskins at the finish of the regular season, but right now Washington's secondary is suspect, what with Tony Peters facing drug-selling charges and Jeris White a holdout.

Cincinnati looked lousy during preseason. Preseason doesn't count; the Bengals still have a terrific offense. I'll go with Kenny Anderson over Jim Plunkett any time the spread is small.

Don't try to get rich in a hurry this season. Parity is truly upon us. There is no great team in the NFL, but the weaker ones aren't terribly weak, either. Even Baltimore will be respectable, thanks to a much-improved defense.

The early weeks are a time to observe as many teams as possible. Pittsburgh's young defensive front is intriguing. So is Seattle's secondary. And what about Tampa Bay's quarterback situation, now that Doug Williams is gone? It has to be better. So does San Diego's pathetic defense.

But let's not get nasty. Another exciting schedule awaits. After nine straight winning seasons, there is reason to be confident, going in. Just remember, it's a tough game, with no sure things.

Experience has taught that the best bet in which I've ever been involved was made by a friend of a friend of mine, eight years ago. He couldn't have made a sharper move at the time.

Heck, I'm still nervous.

Imagine how he must be feeling.