WASHINGTON (AP) _ Excess fat, Buddhist customs and the length of the Japanese digestive tract all work to prevent any quick increase in his country's U.S. beef imports, a Japanese trade authority said Thursday.

Former Agriculture Minister Tsutomu Hata told a Capitol Hill luncheon that Japanese intestinal tracts are longer than those of Americans and thus ''to the intestinal system it will mean a very big change'' to eat more beef.

He also said through a translator that a religious aversion to eat the meat of four-legged animals plus fear about the health effects of a beef diet also are working to head off increased imports from the United States.

The comments from Hata, who now heads a Japanese farm-trade organization, upset the clubby atmosphere of the Mansfield Room adjacent to the Senate chamber. It was called to push the Tokyo government to allow beef quotas to die on schedule April 1 and not seek to renew them.

Hata's remarks brought an immediate riposte from Sen. Phil Gramm, R-Texas, who said Americans had adjusted to the smaller size of Japanese cars because they were more fuel efficient and better built. He said Japanese consumers should have the freedom to decide for themselves whether to buy more beef.

Hata began to reply by saying that it was unreasonable to compare the fuel efficiency of a car ''to the efficiency of a digestive system.''

''The issue is freedom,'' cut in Gramm.

Hata stressed that Japan has been increasing its beef imports over the last few years but did not favor greatly increased shipments.

His comments about the unsuitability of beef for the Japanese because their intestinal tracts are longer brought skepticism from other American officials.

''I've never heard that argument before,'' U.S. Trade Representative Clayton K. Yeutter chortled to reporters. ''I've heard all the rest of them.''

''I think what we heard today was excuses and delays from the Japanese,'' said Rep. Robert F. Smith, R-Ore., chairman of the congressional Beef Caucus. ''We've heard that before.''

Because Hata spoke through a translator, reporters approached him after the session and asked if he meant that Japanese intestinal tracts were literally longer than those of Americans.

''It is factual,'' he said. He said peoples whose diets rely heavily on grains generally have longer digestive systems and that this was also true of the rice-eating Japanese.

He said the extra length means that beef remains in the intestines longer and thus is prone to spoil there.

Lawmakers warned that unless the Japanese lower their beef quotas the United States could retaliate next year with toughened trade legislation.

''This is not a threat,'' Sen. Chic Hecht, R-Nev., told a news conference later. ''It's a hammer over their heads.''