By Jonathan Marcus BBC United States affairs specialist

In what could prove to be a landmark ruling, the US Supreme Court has opened the way for expanded public funding of religious education by allowing the use of vouchers for private schools.

Some legal experts are already calling this one of the most important Supreme Court rulings of the past 30 years

By a five-to-four decision the court upheld the legality of a school voucher programme in Cleveland, Ohio that critics argued made a nonsense of the constitutional separation between church and state.

The whole issue of school vouchers is controversial in the US. The idea is to give parents - especially of children in poor inner city areas - monetary vouchers that they can use towards the cost of tuition in private schools, some of which may be religious.

But the court ruled that the voucher system in the failing school district of Cleveland is not a de facto subsidy of church-run schools.

Some legal experts are already calling this one of the most important Supreme Court rulings of the past 30 years.

Hot debates

Conservative groups - especially on the Christian right - have long argued that parents should be allowed to use public money to pay for private education, whether religious or not.

A US court has recently banned The Pledge of Allegiance at schools

School vouchers have been strongly opposed by teaching unions as an assault on public education but also because of the perceived threat to the cherished notion of the separation between church and state - one of the cornerstones of the US Constitution.

In this bitterly divided ruling the Supreme Court has backed the pro-voucher camp delivering a significant victory to the conservative right.

The issue is complex and relates as much to the crisis in public education in many inner cities as it does to the whole question of religious education.

So far only three states have enacted voucher programmes, Ohio being joined by Wisconsin and Florida.

The Bush administration has strongly backed the idea of vouchers though its own proposals collapsed last year in the face of Congressional opposition.

'Potentially harmful' ruling

The Ohio legislature brought in the voucher scheme in Cleveland in 1995 after the near collapse of the city's public school system.

It provides grants of over $2,000 a year to the families of nearly 4,000 low-income students enabling them to attend religious or secular private schools.

This element of choice underpinned he court's ruling.

Chief Justice William Rehnquist asserted that the Ohio programme was entirely neutral with respect to religion.

But in a dissenting view Justice Stephen Breyer said that the court risked creating a form of religious conflict potentially harmful to the nation's social fabric.