The major leagues hold their 15th annual draft of amateur baseball talent today. So to clear the air of a burning question, the arbitrator's decision is in on the contract battle between the Atlanta Braves and their pick at the top of the 1978 edition:

Bob Horner wins his argument that his six-digit signing bonus counts as part of his pay, as a basis for his 1979 contract. The Braves win in that Horner, who made rookie of the year on only 89 games' worth of National League action (23 home runs) after breaking in June 16, does not win his request to be given free agency on grounds the club's December "conditional" contract renewal was improper.

Is everybody happy?

Well, everybody but Bucky Woy, Horner's agent, who was insisting on $300,000 a year for the Arizona State third baseman (lately moved to first by the Braves).

Also, everybody but all the draft prospects who may well find signing bonuses greatly diminished with clubs scared off by the Horner ruling yesterday from Raymond Goetz, the U. of Kansas law professor-labor arbitrator who heard arguments May 10-11 in New York.

The Braves sought to negotiate Horner's 1979 salary from a floor of $21,000, his rookie wages. Horner and agent Woy Insisted $160,000 in signing and other bonuses paid the 20-year-old athlete (now 21) had to be counted as part of his 1978 pay, making it $181,000 and subject, under major league rules, to 1979 reduction of no more than 20 percent - leaving $146,000 minimum.

Goetz agreed with Horner and Woy, insofar as the signing bonus but not on other extras including payment for college expenses, incentive bonuses and scouting pay to Horner's father. (SECTION) o Atlanta, presuming it goes ahead with the permissible 20 percent cut, this year pays Horner about $128,000 - and sighs with relief.

Owner Ted Turner's December offer amounted to $100,000 anyway.