Las Vegas is not convinced the Baltimore Orioles are the American League baseball team of the '80s -- but it has Manager Earl Weaver pegged.

Bob Martin, the vaunted Head Linesman of the Union Plaza who sets the Nevada oddsmaking pace, makes the Birds no better than a joint fifth choice, with AL East rival Milwaukee, at 5 to 1, to win the pennant. The Yankees and Angels get the cofavorite nods, at 3-1. Texas and Kansas City rate 4-1.

But you have to put up $6 to win $5, says Bob Martin, on Weaver being thrown out of six more games than Oakland's Billy Martin over the season's course. The chances are slimmer on Battlin' Billy completing the season as Charlie Finley's dugout director: Martin is favored, 2-1, not to be around at the finish. All bets off, though, if Finley sells the A's.

The Linesman makes Los Angeles and Pittsburgh 3-1 National League cofavorites, ahead of Houston and Montreal, 4-1; Cincinnati 5-1, Philadelphia 6-1, St. Louis 10-1, San Francisco 25-1, Cubs 60-1, San Diego 100-1, Atlanta 200-1, Mets 500-1.

Boston is 6-1, seventh choice in the AL; the rest strictly for speculators with Detroit and Minnesota 40-1, White Sox and Cleveland 100-1, Seattle 250-1, Oakland and Toronto 500-1.

The $175,000 Washington Star International tennis tournament has been switched from July 14-20 to July 21-21 -- promoters jumping at the chance, evidently, to stage it two weeks after Wimbledon instead of one. Now they can figure on more, and better-rested, big guns hopping aboard. The opportunity arose with collapse of the Louisville Tennis Classic . . .

Hi, neighbor! Martina Navratilova, women's tennis No. 1, has bought Flordon, an eight-acre estate in Albemarle County west of Charlottesville, and intends to move to Virginia. House and grounds include a tennis court; guestimated price, $450,000. . .

New basketball coach at West Point: Pete Gaudet, promoted from assistant to Duke-bound Mike Krzyzewski, Gaudet had been an Army assistant since 1975 after several years coaching Dartmouth (Mass.) High. . .

Richie Adubato, 12-52 since taking over from Dick Vitale as Detroit NBA coach, won't be back next season, the Pistons announced yesterday. . . . But in the NFL, the Chicago Bears have given Coach Neill Armstrong, turning into the third year of a three-year contract, a two-year extension on that, through 1982 -- three more chances to beat the Redskins out of the playoffs? . . .

The Seattle Mariners have capped a long-running dispute with King County, operator of the Kingdome, by filing a 56-point lawsuit -- and one point is that the landlord in effect consigned the American League expansion franchise to bush-league status by making the ballpark too small.

Why, team officials say, if they'd known how close the fences were to be, they would have recruited power hitters instead of building on speed and defense.

The county declares the Mariners $110,000 in arrears in rent, but despite the hassle, Dan O'Brien, club president, insists there is no desire to move the franchise, heading into its fourth year. . . .

The familiar stories have begun from Indianapolis about scalpers' prices for NCAA final tickets; supposedly the $30 tickets command as much as $300-$400 . . . Meanwhile, on your marks -- For tickets to the 1981 basketball finals in Phily's Spectrum, orders must be postmarked April 1 (but not before); drawing if demand exceeds supply to be held April 15. Admission to the March 28-30, 1981 event: $34 a person, limit of four tickets per order . . .

Tough break for George Washington's baseball team, besides a torn-up home field, as GSA installs a drainage ditch on the West Ellipse: Southpaw ace Kenny Lake from Rockville, cover art on the Colonial preseason flyer after a 9-4 campaign last spring and he can hit and play first base too, may be out the season: racked up ligaments in his right ankle.