In what may be the most complex of all the summer's baseball cheating cases, outfielder Billy Hatcher of the Houston Astros said he will tell National League officials he didn't know the bat he was using Tuesday night had been corked.

If the league president, A. Bartlett Giamatti, believes him, Hatcher could avoid getting a 10-day suspension for improperly altering a bat. If he doesn't, it could be a critical blow to the Astros' already fading pennant hopes.

The case is complicated because there's no question Hatcher was using a bat that violated baseball rules. With Gerald Young on first and no one out in the fourth inning against the Chicago Cubs Tuesday night in the Astrodome, Hatcher hit a ground ball to shortstop Shawon Dunston.

But the bat broke and the barrel sailed to Cubs third baseman Keith Moreland. He noticed that the center of the bat had been drilled out about four inches and filled with cork, which presumably makes a ball carry farther. He showed the bat to home plate umpire Dana DeMuth, who took the remnants to crew chief John McSherry. McSherry examined it and, after showing it to Manager Hal Lanier of the Astros, ejected Hatcher from the game.

The bat was shipped to National League headquarters in New York.

Giamatti's decision will be extremely important to the Astros because they've fallen 5 1/2 games behind the San Francisco Giants in the West and because Hatcher has been probably their most consistent hitter, batting .311 with 11 homers and 57 RBI.

The strongest evidence in Hatcher's favor is that the bat didn't appear to be his. It had "45" on one end. Reliever Dave Smith wears jersey No. 45.

"I'm out of bats and grabbed one that was the same model," Hatcher said. "It was one the pitchers use during batting practice, and I had no idea it was corked."

Smith said, "I had someone fix the bat to use in batting practice. But I had no idea that Billy was using it, or how it even got in the bat rack."

Expos 7, Giants 3: Herm Winningham drove in four runs in San Francisco to help Pascual Perez (1-0) to his first major league victory since July 14, 1985.

Pirates 2, Braves 0: The Pirates had one hit in the first six innings against Tom Glavine (1-2) and only three overall. But Mike LaValliere had a two-run double.

Reds 3, Cardinals 1: Bo Diaz's two-run homer with two outs in the eighth inning won the game in St. Louis.

Astros 10, Cubs 1: Kevin Bass went four for four in Houston, becoming the first National Leaguer to homer from both sides of the plate in a game twice in the same season.

Mets 4, Padres 3: Dwight Gooden won a 10-hitter in San Diego, thanks to homers by Howard Johnson and Keith Hernandez.

Phillies 6, Dodgers 2: Mike Marshall and teammate Phil Garner fought before the game in Los Angeles, then their teammates went out and lost their seventh straight. Don Carman gave them only six hits in seven innings.