What's good for the goose is good for the gander in most circles, but on matters of trade they're playing a different theme in the Senate -- what's good for the steer is not good for the sheep.

The recently formed Beef Caucus, co-chaired by Sens. Max Baucus (D-Mont.) and Malcolm Wallop (R-Wyo.), is mounting a campaign to persuade Japan and South Korea to open their markets to more imports of U.S. beef.

The caucus, a brainchild of the National Cattlemen's Association, also is working up language to that effect that it hopes to attach to a major trade bill the Senate is expected to debate this month.

The idea, of course, is free trade and the "even playing field" that agriculturalists complain they're deprived of in world markets.

At the same time, Baucus, whose ranching family raises sheep in Montana, is a chief sponsor of a Finance Committee-approved trade bill amendment that would limit imports of lamb.

Inconsistent? Not at all, Baucus said. "We don't subsidize beef or lamb production in this country. The question is how we can be more effective, and I've found that on beef we have to fight fire with fire," he said.

As for the possibility of a conflict over his sponsorship of a lamb quota that might benefit his family, Baucus said there was "none whatsoever." He added, "It's the only way I can represent Montana -- we have beef, sheep and wheat."

The Reagan administration, however, is strongly opposing the lamb import amendment. The House rejected a similar amendment, opting instead for a study of the effect of imports on producers. New Zealand and Australia, the chief sources of lamb imports, are stewing over the Senate amendment.

"It's the sort of measure that gives protectionism a bad name," an official of the Australian Embassy said. "We regard it as a totally invalid protectionist measure. What's needed is the development of an interest in more consumption, which is still only about 1.5 pounds per capita per year."

A New Zealand trade official said, "We've made our concerns widely known to the administration and the Congress . . . .lamb has to revamp its image in the marketplace. It has to match what James Garner and Cybill Shepherd do for beef. Even Phyllis Diller and Rodney Dangerfield would help."

Both officials, whose countries supply about 10 percent of the lamb consumed here, speculated that current high prices had motivated U.S. growers to lobby Congress for protection against more incursions by importers.

The lamb amendment was the work of the National Wool Growers Association, which has tried repeatedly in recent years to get Congress to adopt a quota scheme similar to a beef import law passed more than 20 years ago.

"The purpose is to put lamb on the same footing as beef," the association's Dan Murphy said. "But there is a prospect of greatly increased lamb imports, and our amendment only sets a floor on imports . . . no lower than what came in last year . . . . The legislation is written in a way that they don't lose."

Murphy said that high lamb prices this year and the ranchers' effort to limit imports were only coincidental, but he said they also were driven by the memory of an import surge when prices were strong in 1978 and 1979.

Baucus assistant Greg Mastel said the trade bill amendment would allow the president to impose quotas if voluntary restraints do not work should imports of lamb go above 29.5 million pounds per year.

"But there are a few major differences between what we're doing with lamb and what is happening on beef," he said. "The lamb import control is predicated on market distortions caused by imports. We're not closing any markets at all. But on beef, Japan, for example, has a flat continual barrier to our product and we want to overcome that."