In the bar rooms of Washington this week there has been a spirit one might see on Wall Street during a booming bull market. These are heady times when everybody is a genius, everybody is a winner.

An eavesdropper could hear dozens of conversations with the identical theme. "I really killed my bookmaker this week," one football bettor was saying the other night. "I knew the Redskins were a lock. I loved the Eagles. I loved the Chargers. I didn't have a loser. What a year this is going to be!"

It would have been unkind to tell the jubilant winner that his accomplishment was not unique. The first week of the 1981 professional football season will be remembered (especially by unhappy bookmakers) as The Week Everybody Won.

It is a popular misconception that the point spread enables bookmakers to attract roughly the same amount of money on each side in a football game. If his books are unbalanced, he can supposedly fine-tune the spread to attract money in the direction he wants.

This is true in Las Vegas, where there are so many sophisticated handicappers with divergent opinions, all looking for a tiny edge. A bookmaker there can adjust a point spread from 6 to 6 1/2 and produce an avalanche of wagers.

But the average local bookmaker will find himself staring every Sunday at an unbalanced ledger. His clients may all gravitate to certain obvious betting situations that a New York gambler dubbed "MOTO selections." MOTO stands for Master of the Obvious. Usually these inviting games are traps, pitfalls for the unwary.

A textbook MOTO was the Philadelphia Eagles favored by 6 over the New York Giants last Sunday. Any casual fan with half a brain assumed that the Eagles would crush the hapless Giants, and the bookies got cramps writing "Philadelphia" on their sheets. What made this MOTO somewhat unusual was that the Eagles did destroy the Giants and bettors all over town were thinking that pro football is an easy game to beat.

There were similar stampedes to bet other games as well, one of which led a local bookmaker to ask, plaintively, "Where are all those diehard Redskin fans?"

Washingtonians may love the Redskins with their hearts, but they looked at the 2-point spread favoring Dallas and bet the detested Cowboys with their heads. "That was the most incredible point spread I've ever seen," one bettor said, reflecting the general sentiment. "How was that offensive line going to contain the Dallas front four?" Ironically, there was far less support for the Redskins in their home town than in Las Vegas, where a lot of "smart money" showed up for them. The local bookies got creamed.

When the money was pouring in on the Eagles, the Cowboys, the Lions and some other popular teams, the bookies had no realistic defense. It's too risky to adjust a 6-point spread upward to 7 1/2, because that invites gamblers to bet the other team and win both ways if the final margin winds up at 7. So they could only pray that the public's opinions would be wrong, as the public's opinions usually are.

But the public wasn't wrong last Sunday, and the bookies had to console themselves with the knowledge that the law of averages hasn't been permanently suspended. "I know the percentages are going to work in my favor," a bookmaker said. "I just hope my people don't blow all their money before it does."

For a couple more days, though, those bettors can keep on celebrating, feeling invincible and emboldened. But as soon as next Sunday, they probably will start to remember that betting football is not as easy as it now seems.