Idaho Gov. Cecil D. Andrus (D) yesterday vetoed the most restrictive abortion law passed in recent years by any state legislature, derailing plans by supporters of the measure to force a Supreme Court challenge to the legality of abortion.

Andrus, who said he is opposed to abortion, said he agonized over provisions of the legislation but concluded that the bill does not provide a woman and her family any flexibility in cases of rape and incest.

"The bill is drawn so narrowly that it would punitively and without compassion further harm an Idaho woman who may find herself in the horrible, unthinkable position of confronting a pregnancy that resulted from rape or incest," he said.

Andrus waited to veto the bill until the legislature adjourned for the year yesterday, eliminating any chance that the veto could be overridden.

Abortion-rights advocates had said the bill was unconstitutionally restrictive and had promised an immediate legal challenge if Andrus signed it into law. That would have given antiabortion forces the court test they hoped would lead to the overturning of the Supreme Court's landmark 1973 Roe v. Wade ruling that recognized a constitutional right to abortion.

The measure, drafted by the National Right to Life Committee, was designed to attract the support of Justice Sandra Day O'Connor, the key vote on the Supreme Court on the divisive abortion issue.

Kate Michelman, executive director of the National Abortion Rights Action League, yesterday praised Andrus, who she said was in "a no-win situation." She said, "He put his personal feelings aside and refused to rob women of the personal decision that rightfully belongs to them."

But Michelman warned, "Though this is a major victory and demonstration of 'pro-choice' strength, it does not mean that the threat to choice has been eliminated. With every bill we defeat, another threat arises in another state."

Nancy Myers, communications director for the National Right to Life Committee, said Andrus "completely abandoned his principles -- he can no longer be considered 'pro-life.' "

She said his "excuses won't wash with the people of Idaho. This law was passed by both houses of the Idaho legislature. It's a reasonable measure. People want it. It would be upheld by the court." Myers said the veto will be "a shot in the arm," galvanizing antiabortion forces nationally. "This doesn't end with Idaho," she added. "Other states will consider this law this year or next year."

Telephones lines into the governor's office were jammed yesterday. Since the bill banning abortion as a method of birth control cleared its first major legislative hurdle in the House three weeks ago, more than 21,000 telephone calls, letters and petitions have gone to Andrus's office, according to his aides.

The tally ran about 2 to 1 in favor of a veto of the bill, which would have banned more than 90 percent of the abortions now performed legally in Idaho. Last year 1,650 were performed there.

Some abortion-rights groups, led by the National Organization for Women (NOW), had called for a boycott of Idaho products, particularly the state's famous potatoes, if Andrus signed the measure. Yesterday, NOW President Molly Yard congratulated the governor. "He clearly thought the bill was extreme and he was right," she said.

Andrus, who had reaffirmed his longstanding opposition to abortion except in cases of rape, incest or a threat to the life of a woman when he announced his candidacy for a fourth term last week, first publicly expressed doubts about the antiabortion bill Thursday. He said he was concerned that women who have been raped, victimized by incest or faced a threat to their lives might not be able to obtain an abortion.

Speaking at a news conference in Boise yesterday, Andrus said he consulted on the issue with legal scholars of both political parties who said there was not the "remotest chance" of the Supreme Court upholding such a law. He also cited the financial burden to the state to defend the bill in court.

The bill called for outlawing abortion except in cases of non-statutory rape reported within seven days, incest if the victim is under 18, severe fetal deformity or a threat to the life or physical health of the woman.