The nationwide interest in the Louise Woodward trial and its dramatic sequel has not been matched in the United States since the O.J. Simpson case but child care, rather than the workings of justice, is the main concern.

With two-thirds of American women with children under six now at work, the idea that a child-minder could murder her charge had sent chilling reverberations across the country. Judge Hiller Zobel's decision to reduce the second-degree murder conviction to manslaughter will be seen to be more appropriate in the case of a young child-minder under stress. But giving her a sentence which allows her to walk free will prove controversial.

Americans will not want a signal sent that "shaking" which results in the death of an infant does not merit any punishment. But as the judge pointed out when sentencing her to time served, she now has been convicted of a felony which will stay on her record and she has served nine months in prison, so this is by no means an acquittal.

The judge, a scholarly lawyer and navy veteran, was under enormous pressure, especially from Britain, to set aside the murder verdict but he is not the kind of man to let public opinion influence him in matters of law, as he said in the preface to his decision. One concession he did make was to put his judgment on the Internet and make it as widely available as possible. In this way, he wanted to let his decision get through to the public in its original form and not as mediated through TV, newspapers and legal pundits.

Jurors in the trial have expressed relief that the judge has reduced the murder verdict. The prospect of a 19-year-old British girl serving life imprisonment clearly disturbed some of the jurors but did not prevent them from going along with a second-degree murder verdict which presumes malice or intention to harm on the part of the accused.

Manslaughter was the obvious compromise, but that option, which was closed to the jury, was revived by the judge, making observers wonder why he did not allow it to go as an option to the jury during the trial itself. This was requested by the prosecution, which felt diminishing confidence in making the murder charge stick.

Politics has also come into the debate on the case because new, tougher welfare rules are driving single-parent mothers to seek jobs or risk losing the modest support payments from state agencies. Even before the Woodward case, child care was becoming a pressing issue and Mrs Hillary Clinton had organised a White House conference on the subject which, by coincidence, took place during the trial. Senator Edward Kennedy used the conference to propose greatly increased federal spending on child care.

There was almost universal acknowledgement that the justice system in Massachusetts had not treated Louise Woodward fairly and that a murder verdict, even second degree, was inappropriate. But equally, unlike in Britain, public opinion here seemed convinced that the au pair had some responsibility for the death of eight-month-old Matthew Eappen and that some punishment was required.

Some 12,000 American families use foreign au pairs each year to look after young children. An acquittal of Louise Woodward would have sent a dangerous signal that "shaking" difficult babies could be tolerated.

The manslaughter conviction shows that au pairs, like any other child-minders, will be held responsible for their actions with small children even if they do not intend to do serious harm. But first reactions to yesterday's decision showed that some of the American public is unhappy that Louise Woodward has now walked free and has escaped a more serious sentence. Manslaughter carries a maximum sentence of 20 years but no minimum.

The case has focused new attention on the au pair system which is now relied on by many middle-class parents as the only affordable way to have full-time child-minders. Various attempts to tighten up rules for the au pair "cultural" programme, run by the United States Information Agency, have been resisted by working mothers and the au pair agencies.

Matthew Eappen was the third child to die in au pair care since the present programme was approved by Congress in 1986. After a Dutch au pair was accused of shaking a baby to death in a home in Fairfax, Virginia, in 1994, Congress tried to tighten up the rules by changing the minimum age for au pairs to 21 and their weekly working hours to 30 instead of 45, but the parents and au pair agency lobbies campaigned against the reforms, which were dropped.

Since the death of Matthew Eappen, new measures have been approved which require more training and increase the pay but the hours stay the same and the minimum age remains at 18.

Thus the contradiction in the present system - in which au pairs are ostensibly on a "cultural exchange" programme in return for light duties around the house, while the parents demand full-time childminders - remains.

As the New York Times put it in an editorial called "The Nanny Verdict": "The fundamental problem is that families hiring au pairs are looking for affordable, reliable child care while the young women who come from abroad to fill the slots are looking for adventure and cultural enrichment. Reconciling these two desires is difficult in the best of circumstances, impossible in many. The Woodward case shows how that clash can destroy lives."

The columnist, William Safire, writes: "The issue wrenches the psyche of families. As families get smaller, single-parented and ungrandparented, we realise that even strange relatives can be better than relative strangers."

The huge interest in the Louise Woodward trial has wider cultural reverberations than the concerns of parents with young children entrusted to minders while they work.

The millions who followed the trial live on the Court TV channel were drawn into passing judgment themselves as if they were in the place of the jury, commentators note. Many as parents felt they had their own expertise as to how babies should be treated and the dangers of "shaking".

The intense debate about the distinctions between first and second-degree murder and manslaughter among lawyer pundits on TV chat shows helped to turn many of the public into barrack-room lawyers.

The debate has also focused on the tactics of prosecution attorneys across the US who routinely, it seems, overcharge as a means of pressure to get the accused to accept a plea-bargain on a lesser charge. This is a practice not used in Britain, Ireland or other European countries and it clearly has the risk of making innocent persons choose the lesser of two evils.

Louise Woodward and her defence team surprised almost everyone by rejecting the possibility of the jury considering a manslaughter verdict as a compromise, but for nonAmericans this was logical if you believe in your own innocence.

In the US that way danger lies, as Ms Woodward has discovered. Judge Zobel has wisely intervened as he was entitled to do. So the US justice system has more flexibility and compassion than its critics have been maintaining.