SYDNEY, Australia (AP) _ Tap water in the city that will hold the 2000 Olympics will not be safe to drink for up to six months, sources at the Sydney Water utility warned in comments published today.

Residents and visitors have been told not to drink or otherwise ingest the water unless it has been boiled for at least a minute because of contamination by the microscopic organisms giardia and cryptosporidium.

Testing has shown contamination at wildly fluctuating levels, and the warnings officially will stay in place for most of Sydney's 3.7 million residents until Sept. 19.

But The Sydney Morning Herald reported today that sources at Sydney Water conceded that water from the city's main source, the Warrangamba Dam, will remain suspect until March.

Giardia, normally spread through human or animal fecal matter, can cause diarrhea and other gastrointestinal problems. Cryptosporidium causes flu-like symptoms and can kill people with weak immune systems.

The federal government stepped in today to try to minimize the negative effect of the water contamination crisis.

Prime Minister John Howard _ who said the first family was drinking boiled or bottled water at their home _ offered the New South Wales state government any scientific or other assistance federal agencies could provide.

``It's embarrassing but equally it's a public health development that could overcome any major city in the world,'' Howard told Australian Broadcasting Corp. radio.

Tourism Minister Andrew Thomson called an emergency meeting of industry leaders to formulate a strategy to combat the effect on Sydney's international image.

``This is the worst thing that has happened to Sydney's reputation in living memory,'' Thomson said. ``It has to be fixed soon. Otherwise there will be real damage inflicted in the long term.''

Canadian tourist Morreen Prior agreed. Hearing about the crisis, she bought bottled water at home in Toronto and was drinking it today in front of the Sydney Opera House.

``The hotel told me not to drink the water,'' she said. ``It's really embarrassing for Sydney.''

Outbreaks of giardia and cryptosporidium in the water were reported in late July and again last week.

The Health Department has said the level of cryptosporidium found in water samples was 12 times higher than the levels reported in an outbreak in Milwaukee in 1993, the worst such outbreak ever recorded in the United States. That contamination contributed to the deaths of about 100 people, many with immune systems already weakened by AIDS or cancer.

Other testing periodically turns up minimal levels or no parasites.