The Senate Appropriations Committee yesterday rejected a House amendment to stop the Food and Drug Administration from banning saccharin for the next 15 months. It acted after receiving assurances that Congress would be able to act on saccharin later this year.

By then Congress will have had time to consider the issue "calmy and rationally," said Sen. Thomas F. Eagleton (D-Mo.), who proposed rejection of the House amendment.

Meanwhile, in San Francisco the American Medical Association voted in favor of keeping the aritificial sweetener in diet food and drinks - with merely a label warning of possible harm - until there is clearer proof that saccharin causes cancer.

The AMA also urged repeal of the controversial Delaney Amendment, which provided part of the basis for the FDA's proposal in March to ban saccharin in food and beverages, while allowing its sale as an over-the-counter nonprescription drug.

The Delaney Amendment has been interpreted as requiring removal from the market of food additives shown to cause cancer in humans or animals.

The FDA proposed the curb on saccharin, widely used as a sugar substitute by dieters and diabetics, on the basis of studies in which short-term feeding of the substance in large amounts caused cancer in animals.

The first congressional action against the FDA's proposed ban came Tuesday when the House amended a $13.7 billion agriculture appropriations bill to ban use of any of the funds for promulgating or enforcing a saccharin ban until Sept. 30, 1978.

But yesterday the Senate Appropriations Committee voted unanimously to reject the House proposal after Eagleton said separate legislation likely to include an 18-month moratorium on action against saccharin will be before Congress later this summer - well before any ban is imposed.

Eagleton said he has been assured by FDA officials that the ban, in any case, would not be imposed before Oct. 1.

Eagleton said the legislation would give the FDA more freedom to cope with potential health hazards from saccharin than the House amendment does. "What we need most on this saccharin issue is more time to calmly and rationally consider the information at hand," he added.

Eagleton said Sen. Edward M. Kennedy (D-Mass.), chairman of the Senate Health and Scientific Research Subcommittee, plans to bring a bill dealing with saccharin to the Senate floor next week. The bill is expected to include an 18-month delay on any saccharin ban and a study by the National Academy of Sciences on the effectiveness of the Delaney Amendment.

The AMA, in its action yesterday, urged Congress to require that no additive be banned unless it clearly causes cancer in humans or causes cancer in animals that have received amounts of the additive equivalent to daily human doses.

The association, most of whose, 172,830 members are practicing physicians rather than scientists, rejected arguments by many cancer scientists that that it is necessary to test animals with large doses over a short period to duplicate the effect of continued exposure of humans to small amounts of cancer-causing substances.

Pending a change in the Delaney Amendment, the AMA's House of Delagates decided by voice note to urge Congress or the FDA to permit the sale of saccharin "with labeling warning of the potential increase in the incidence of cancer in animals and humans based on the currently available evidence."

Arguing that many severly diabetic patients need artificial sweeteners to stay on prescribed diets, Dr. Alex Scott of Junction City, Kan., said, "I personally hope my diabetic patients living long enough to get cancer of the bladder from saccharin."