The Supreme Court yesterday heard debate on what is expected to be its most controversial question this year: whether Congress or states can ban federally financed abortions for poor women.

Solicitor General Wade McCree argued for the government that the fund cutoff was a legitimate tool to help "preserve human life and encourage childbirth." It did not, McCree contended, actually prevent women from obtaining abortions and even if it did cause difficulties for some women. McCree said, Congress has no obligation to "solve every single social problem."

The Hyde amendment, which cut off the funds, is a "classic case of discrimination," opponents responded yesterday. It singled out a specific medical procedure and denied it to a specific class of people. "Acting on the idea that abortions are to be stopped," said Northwestern University law professor Robert W. Bennett, Congress and many state legislatures zeroed in on "a helpless group of indigent citizens that can most easily be ignored."

Congress first cut off most of the money in 1976 and has continued to do so, in modified ways, ever since. Only those pregnancies that threaten the women's life or result from rape or incest are now exempted. The Supreme Court temporarily restored the funding two months ago while it considered lower court decisions from New York and Illinois that ruled the ban unconstitutional.

Lawyers from all sides argued those two cases yesterday in familiar terms. But it was the public's first glimpse of the thinking of some of the justices, who sometimes use oral arugments to debate one another.

While such glimpses can be misleading, the differences were predictable yesterday. Chief Justice Warren Burger and Justices William Rehnquist and Potter Stewart asked questions supportive of Congress, while Justices John Paul Stevens, Thurgood Marhsall and William Brennan seemed hostile to the Hyde amendment. Justices Byron White and Lewis Powell gave few clues to their current views, and Justice Harry Blackman, who wrote the court's original 1978 opinion legalizing abortion, said nothing.

"Shouldn't it be left to Congress?" Stewart kept asking Hyde amendment opponents yesterday. "Are you stating that the court should direct Congress on how it exercises its spending power?" asked Burger.

"Doesn't a legislature have the power to make value judgments" involved in a decision to ban abortion funding? the chief justice continued.

"Don't we have to consider the expressed will of the Congress?" Rehnquist asked.

Stevens, on the other hand, suggested that the Hyde amendment actually "denied some women abortions. Don't we have to assume," he asked, "that some women will suffer health damage" as a result.

During the court's 1977 term, the justices ruled 6 to 3 that a state is permitted to cut off funds for elective abortions -- those that may not be medically necessary.

Justices and lawyers yesterday took pains to distinguish the current cases -- which ban funding for medically necessary abortions -- from the 1977 decision in Maher vs. Roe, a suggestion that the distinction may loom large in the final decision.

The cutoff of money is "in effect coercing indigent women into having abnormal childbirths, perhaps leading to death," said Bennett, arguing the Illinois case.

The arguments attracted about 50 demonstrators -- pro and con -- outside the courtroom and the years' longest line of spectators waiting to hear the discussion inside.