French hospitals risk collapse as the government tries to impose its flagship 35-hour working week law on already over-stretched doctors and nurses, health unions warned yesterday.

The hospitals are part of a health service that was last year rated by the World Health Organisation as the best on the globe for quality of care.

The unions dismissed as wholly inadequate a promise by the social affairs minister, Elisabeth Guigou, to recruit 40,000 new nurses to plug the holes left by the shorter working week, and threatened strike action before the end of the year unless their concerns were addressed.

"The situation is explosive," said Rachel Bocher, the psychiatrist president of a leading health workers' union, INPH. "Hospitals lack staff, funding and the capacity to reorganise."

Threatened industrial action over the problems caused by the 35-hour week in the health service could well be mirrored by more widespread discontent throughout the public sector in the run-up to presidential and parliamentary elections due next spring.

The Socialist-led government intended the 35-hour week primarily as as a means to create private-sector jobs, and introduced it with considerable and unexpected success last February in companies of more than 20 people.

The Socialist prime minister, Lionel Jospin, now aims to apply the controversial legislation to the public sector by January 1 - but without shattering spending targets by putting too many more people on the state's payroll.

In most parts of the traditionally bloated French civil service, that objective, while it may lead to some grumbles, looks eminently attainable. In the country's hospitals, it will be rather harder to achieve.

Hospital doctors and nurses, although better off than their British counterparts (France spends 9.8% of GNP on its health system, compared to 6.9% in Britain), have long complained of deteriorating conditions. They last launched industrial action in 1999.

"My staff routinely work five, six, seven extra hours a week, and never take time off in lieu," said Christine Picot, head of the maternity ward at Montreuil public hospital in the Paris suburbs. "We can't even operate a 39-hour week as we are supposed to. Talk of a 35-hour week is fantasy."

According to government figures, the French hospital service, which employs some 780,000 people, is already short of some 10,000 to 15,000 staff, mainly nurses. Health unions say that even without taking the 35-hour week into account, double or triple that number are needed to ensure the service runs as it should.

But with the nursing profession suffering recruitment problems around Europe, even the current vacancies have proved impossible to fill. The government has been forced to import 8,000 Spanish nurses, and to launch a campaign aimed at enticing back some of the 50,000 disillusioned French nurses who have left the profession in recent years.

"Where are the 40,000 supposed to come from who will make it possible for us all to work a shorter week?" asked Sandrine Orsucci, an anaesthetist's assistant at the Pitié-Salpetriere hospital in Paris, who earns, with seven years' experience, £13,000 a year.

"Even if they increase the number of places at nursing schools, there's no guarantee there will be any candidates. This whole project is a mirage, it's utopia. They are going to have to do far, far more."

The government is, however, unwilling to go much further. Ms Guigou's promise of extra staff angered the finance minister, Laurent Fabius, who now has to find an extra £1bn in an already strained 2001 budget that foresaw the creation of just 11,500 new civil service jobs as a result of the 35-hour week.

Union leaders, who have called an initial nationwide day of action on September 20 for all but emergency staff, point out that extra personnel are only one part of their demands.

"What is really needed is a complete overhaul of hospital structures and organisation," said Ms Bocher of the INPH.

"Otherwise, no matter what extra resources are flung at us, the whole thing will be a waste of time and effort and our hospital system will crumble beyond repair. It is only the staff's dedication that is holding it together at the moment."