From our correspondent: Washingon, January 22

In a long-awaited decision the United States Supreme Court ruled today that a woman has a near-absolute right to an abortion, but only in the first three months of pregnancy.

During the later stages the State has an increasing power of intervention, the court ruled by a seven to two majority; and during the last "trimester" can refuse to allow the operation.

The decision, which came today as part of a lengthy ruling which declared the Texas and Georgia anti-abortion laws unconstitutional, has been generally welcomed by liberal groups here. Mrs Lee Giddings, of the National Association for the Repeal of Abortion Laws, said today she was "absolutely thrilled."

But one of the two dissenting Supreme Court justices, the Nixon appointee, Justice Byron White (the other dissenting justice was also a Nixon appointee, Mr William Rehnquist), later criticised the verdict as "improvident, extravagant, and an exercise of raw judicial power."

In his ruling, Justice Garry Blackmun said that during the first three months of pregnancy "the abortion decision and its effectuation must be left to the medical judgment of the woman's doctor." After that, the State "in promoting its interest in the mother's health" may regulate the abortion procedure by, among other things, making laws regulating the doctor's terms of reference.

Only in the third three-month period, when a foetus could presumably live, if there was a premature birth, can the State "regulate or even forbid abortion." The justices ruled the State could intervene thus "where it was necessary, in appropriate medical judgment, for the preservation of life or the health of the mother."

In the overturning of the originally anti-abortion laws of Texas and Georgia the court has, in effect, put an end to the illiberal regulations that exist in 45 other states. Only New York, California, Alaska, Hawaii, and the District of Columbia have truly liberal laws and these - especially in New York State - are currently under immense pressure from Roman Catholic organisations and lobby groups such as Right to Life.

Thirty states have laws similar to those in Texas which abortion make a crime unless it is necessary for the saving of a mother's life; 15 states have laws similar to Georgia's which allowed abortions to be performed only after a pregnancy caused by rape or where there was a possibility of mental or physical defects to the child.

In New York State, terminations are virtually available on demand - for about $200 (£85) - for women who are up to 20 weeks pregnant. Here, in the district of Colombia eight abortion clinics have opened up since the laws were changed in 1971, and the average cost of termination is around $175 (£75).

Maryland and Virginia, the two states which border the District, have very strict laws, and so most terminations performed in the city are on out-of-state women who simply drive across the District line, stay in a clinic for the mandatory 24 hours, and then return home. As elsewhere, though, abortion is essentially a middle class phenomenon - the poor blacks who make up about 75 per cent of Washington's population have little or no access to the clinics.

The one dissenting voice raised today at the Supreme Court ruling came form the Women's National Abortion Action Coalition, which condemned the "artificial and arbitrary" time limits imposed by the judges. A spokesperson, as they say here, said that "a woman should always have an absolute right to determine what happens to her own body." Harsh reaction is also expected, of course, form the Roman Catholic Church, and other anti-abortion lobby groups.