The Senate yesterday voted 55 to 30 to kill tough House curbs on free federal abortions for low-income women.

Instead, it approved language sponsored by Sen. Edward W. Brooke (R-Mass.) allowing free abortions for needy women under the Medicaid program in a wide variety of situations. They would include cases where the woman and her doctor conclude that abortion is "medically necessary," a term several anti-abortion senators called so broad that it would allow "abortion on demand."

The abortion issue, one of the most inflamatory to come before Congress in years, produced a series of fights and a lengthy House-Senate impasse last year, and threatens to produce the same scenario this year.

Earlier this year, the House added to the fiscal 1979 appropriations bill for the departments of Labor and Health, Education and Welfare a ban on federal funding of abortions except "where the life of the mother would be endangered if the fetus were carried to term." This would knock out virtually all federal Medicaid abortions, since there are only a small number of cases wherre pregnancy endangers the woman's life.

Brooke, arguing that this would forbid federally funded abortions even where the fetus "may be deformed or bears an incurable disease," or where pregnancy threatens the mother with a severe, if not fatal disease, proposed a much broader standard. Under his amendment, federal funding of abortions would be allowed where the woman's life were endangered or in case of rape or incest or where "medically necessary."

He called a ban on Medicaid abortions gross discrimination against low-income women, who can't afford private abortions and would have to resort to "coat hangers."

The Senate Appropriations Committee, in reporting the $56.5 billion funding bill, adopted the Brooke language. Last night, when Sen. Orrin G. Hatch (R-Utah) attempted to kill the Brooke language and put the House wording in, Brooke won on the 55-to-30 vote.

So far, the scenario is almost exactly the same as last year. The House put in a tough abortion ban, the Senate loosened it. Last year, a compromise was finally worked out permitting free federal abortions to save the life of the mother, or in cases of rape or incest or where the mother would suffer severe permanent physical health damage from the pregnancy.

This language is in existing law, but whether the same final compromise will be reached isn't clear.

The existing language expires Sept. 30 at the end of fiscal 1978. Any new language would cover the fiscal year starting Oct. 1. At one time, the Medicaid program funded 260,000 abortions yearly for low-income women, but this has fallen since Congress began adopting anti-abortion riders to the Labor-HEW funding bill.

After voting on the abortion issue, the Senate passed the $56.5 billion funding measure.

Earlier, the Senate killed a move to chop 9.6 million employes of small businesses from coverage under the occupational safety rules. The vote, 47 to 46, came on an amendment by Dewey F. Bartlett (R-Okla.) who said it would stop Labor Department efforts to "harass historically safe small business."

His amendment would have exempted from the safety regulations certain categories of small businesses provided that they had 10 or fewer workers and the accident rate for that category was 7 per 100 annually or less. Barlett said that only businesses with 9 or more accidents per 100 were considered really hazardous by the Labor Department, so his amendment wouldn't create many dangers.

However, William D. Hathaway (D-Maine) said, "Whether a worker is employed in a place which has nine employes or 900 employes, he's entitled to a safe place to work."

Also defeated, 53 to 40, was an amendment by Charles McC. Mathias Jr. (R-Md.), to provide $856.4 million for school impact aid instead of the $799 million recommended by the Appropriations Committee. The president and House had recommended the same amount as Mathias wanted, but the Senate Appropriations Committee cut it in an economy move.