London — How does the state help families best? * By providing a free state school reasonably close to home - or by giving parents a voucher instead, worth $:800 ($1,200) at a primary school, $:1,000 ($1 ,500) at a secondary school, and $:1,200 ($1,800) in the six form (final grade)?
Those are the approximate costs for one child for a year in a British state school. Parents would be able to redeem the vouchers either at a state school, or, if they wished, might be able to add to them and send their children to a private school.
* By leaving curriculums untouched - or by introducing classes on child development, marriage, and parenthood?
* By leaving income taxes unchanged - or combining new tax and benefit systems to enable working parents to afford adequate child care?
* By encouraging social workers, teachers, doctors, architects, and others to undertake more professional state and social welfare work - or by questioning the impact and power of such professional occupations?
''The concept of the professional, with his claim to unique understanding of his area of practice, when incorporated in a state bureaucracy can also lead to (services) driven by professionals' views of what ought to be provided rather than consumers' views of what they want,'' says a recent government working paper here.
* By providing more state housing - or encouraging tenants to buy, or develop homesteading plans, or to have more public housing locally managed?
* By building more state-run old people's homes - or rewarding families via taxes and benefits for taking care of their own? What about encouraging community-based short-term care, even as short as a single day?
These are some of the controversial questions being asked by a new British government advisory body called the Family Policy Group at 10 Downing Street.
In effect, the group is challenging the fundamental concept that the existing , proliferating welfare state is to be accepted as an inevitable part of modern life.
If Prime Minister Margaret Thatcher wins the next election here and starts to carry through even some of the new ideas, Western Europe and the United States could be set a startling example.
At the same time, British society could experience some profound changes.
There is still a long way to go, and much more refining, polishing, and ''selling'' to the electorate to be done. Some of the plans may never get off the ground, especially at a time of mass unemployment when more than 3 million people in Britain alone are drawing state unemployment benefits.
Yet a new debate has been solidly joined.
The planners, led by author and former journalist Ferdinand Mount, agree that the state must provide some essential services, including health, education, roads, police, etc. But in social areas they think people should be allowed more choice for themselves, more encouragement to make their own decisions.
The opposition Labour Party and such groups as the National Union of Teachers are up in arms against the group, which was founded last year. The political center and far left, as well as many social groups, are alarmed that Prime Minister Margaret Thatcher wants to dismantle the welfare state.
For instance, the National Union of Teachers argues that vouchers would put education at the mercy of parents' ability to pay. It says the program would encourage private schools.
Six local authorities have been involved in pilot plans, but many questions have proven difficult. Should the vouchers be redeemable at private schools? (Education Minister Sir Keith Joseph believes that they should.) Should there be a means test? How could private schools be prevented from raising their fees to take advantage of the vouchers?
Controversy also surrounds suggestions that mothers be encouraged to stay at home rather than go out to work, and that people should take more responsibility for their own pensions, with the state providing only a minimal safety net.
Most women, critics say, work today for economic reasons: They need the cash. Mrs. Thatcher wants the British to return to the Victorian virtues of hard work, prudence, and self-reliance. But, critics counter, in Victorian times, women did not work.
The French pay almost $1,500 for the birth of a third child, and for each following child, and add allowances and supplements - yet the sector of the work force growing fastest is still French women aged between 25 and 54.
A detailed argument against the pensions idea comes in a new book, ''After the New Right,'' by Social Democratic Party analyst Nick Bosenquet.
It is mistaken, Mr. Bosenquet says, to base welfare on ''market relationships'' because ''the most basic relationships are not market relationships.'' He says women live 10 years longer than men, on average, but earn less than men and would work less anyway if the new ideas took hold. Thus women would find only small pensions ''in the marketplace.''
As for caring for the elderly, critics say that in Victorian days, those over age 75 accounted for one person in 76. Today they represent 1 in 16, and families can no longer cope.
Those familiar with the new ideas and the Family Policy Group reply that their efforts are less startling than they have been made to appear.
Some ideas first surfaced earlier this year in a spectacular ''leak'' of early working papers to the center-left Guardian newspaper. The Labour Party, seizing on the issue, recalled that another leak the previous autumn had also caused a storm - a paper from the Central Policy Review Staff advocating deep cuts in health services, pensions, and education.
The prime minister, who supported the paper, was forced to disown it in public when protests about cuts in the health service mounted.
Now ideas that could have the same cost-cutting effects have been leaked again, and the Labour Party says cutting expenditure is the real, undercover reason for the Family Policy Group.
Group leader Ferdinand Mount argues in a new book, ''The Subversive Family,'' that the family is far from dying. More people in Britain are marrying at some point in their lives than at any time in the past century. And most stay married. More and more are remarrying, too. By 1979, one-quarter of all marriages involved a person married before. In 1900 the figure was only one-eighth.
Divorce rates are certainly soaring, but that is due, Mount writes, to:
* Legal aid.
* The Divorce Reform Act of 1969, which introduced grounds of ''irretrievable breakdown,'' divorce by mutual consent after two years' separation, and by the wish of one partner after five years apart.
* Welfare for divorced women so that poorer couples no longer have to stay together to survive.
* People marrying younger into ill-matched marriages.
Other groups are urging the government to adopt different policies to help the family, too. They include: paying invalid-care allowances to married women (they are currently paid only to men and single women); family courts to settle family disputes; more day care for children and the elderly; subsidies to ensure that the elderly are linked to the outside world by telephone.