Skipper Ted Turner has a couple of new downs to go with his America's Cup ups: his Atlanta Braves have bade farewell to pitcher Andy Messersmith until next year, his Atlanta Hawks have kissed off forward Bill Willoughby for good.

Turner's average in baseball's free-agent signing league was dismal enough with the year's suspension he earned for tampering before he landed Gary Matthews from the Giants. It sags further with the decline of his pioneer pickup, the original free-agent test case Messersmith, who either came from Los Angeles with or quickly developed elbow problems. Formerly bandy Andy went 11-11 with Atlanta in 1976, was of only intermittent use in '77 and none after July, and his woes culminated this week in surgery for removal of bone chips. When the righthander comes back, assuming he can, he'll be going on 33.

Willoughby, on the other hand, is only 20. After going to all that trouble to draft Willoughby out of high school, making him the youngest player ever in the NBA in 1975, the Hawks let him go yesterday - just as he figures to be blossoming, a la 76er Darryl Dawkins.

The Hawks let him go for a second-round draft pick to the Buffalo Braves, whose new coach, Cotton Fitzsimmons, was his original NBA guru.

Bullet GM Bob Ferry reports center Wes Unseld agreed to contract terms and expected to sign today (probably for two years) . . .