The odds are 2 to 1 that President Carter won't seek reelection, but if he does the odds are 2 to 1 against his winning, according to Jimmy (the Greek) Snyder, the nation's best-known oddsmaker.

"People don't understand him, they don't understand what he's doing," Snyder said after two days of sniffing the political winds in Washington. "He doesn't communicate, and here he's on TV more than any president I remember."

If this were 1980, the presidential race would be between Ronald Reagan and Sen. Edward M. Kennedy (D-Mass.), Snyder said in a interview.

"There's no question in my mind that the Republicans would go with Reagan," he said. "Sure they say he's 67 years old, but he speaks well and he looks good."

The former movie star and California governor is a 20 to 1 favorite over the only announced Republican presidentail candidate, Rep. Philip M. Crane, a conservative from Illinois. "I can't see anyone beating Reagan," Snyder said. "If he wants it, it's his for the taking."

The Las Vegas oddsmaker, is less certain about the Democrats. For one thing, he isn't ready to write off Carter.

"As long as you're president you've got a chance," he said. "It's like being quarterback. If you call the right play, you're back in the ballgame."

Kennedy, however, is the odds-on favorite in Snyder's mind. Chappaquiddick is no longer the issue it once was, Snyder said, referring to the July 1969 incident in which a car driven by Kennedy plunged off a bridge on Chappaquiddick Island, Mass., and the body of Mary Jo Kopechne, a 28-year-old secretary, was found in the car.

Polling he did in 1972 found that 67 percent of the women interviewed would vote against Kennedy. Snyder said, "Four years later it was down to 52 percent. Last year it was under 40 percent. People are growing up. They've forgotten about it. Nobody thinks he's guilty anymore except Jack Anderson and me."