OAKLAND, JULY 15 -- National League President A. Bartlett Giamatti has appointed a five-man owners committee to study expansion, it was learned this week.

Giamatti named John Madigan of the Chicago Cubs' board of directors as chairman of the group and said he believed the league would expand sometime in the next decade, probably the "mid-1990s."

He appointed the committee about a month ago after some National League owners asked to "revisit" the question of expansion, Giamatti said.

"This is a subject for discussion this year and next," he said. "If there is expansion, I would think it will occur in the 1990s. I don't believe it'll happen in the 1980s."

Baseball Commissioner Peter Ueberroth said, "I think it's coming. I'm pleased that it's not a once-a-year subject at cocktail parties anymore."

But American League vice president Bob Fishel cautioned against overenthusiasm, saying, "It's not on the verge of happening" anytime soon.

The committee's establishment is the first positive step toward expansion since an overwhelming majority of owners rejected the idea in December 1985, several owners citing lack of a timetable and strong feelings against expansion.

Those sentiments apparently have eased, and several baseball sources said the American League might even expand first so it could regain a balanced schedule.

Such a move by the AL would bode ill for Washington's franchise hopes because the Baltimore Orioles own American League territorial rights. However, if the National League expands, many baseball sources consider Washington and Denver prime candidates, followed closely by Phoenix and Tampa.