Fairfax City Manager George E. Hubler Jr. yesterday imposed an emergency ban on all car washing and lawn watering in the city on Saturday and Sunday, and said police will ticket violators.

Hubler imposed the mandatory ban because requests since late May for a voluntary moratorium on weekend car washing and lawn watering have not relieved water shortages and low-pressure problems in the Northern Virginia city, according to city spokesman Robert A. Becker.

As a result, Becker said the city periodically has had to use water from three emergency lines owned by the Fairfax County Water Authority.

He said the city's two water-storage tanks, each 100 feet high, hold a total of 5 million gallons of water. Normally, the water level in the tanks is 90 feet, but it has been in the low 60-foot range most of this week, Becker said.

"That's near critical," Becker said. "We just can't have that."

Asked if the 21,000 Fairfax City residents can water their lawns today, Becker said, "We'd rather they did not water them at all."

Fairfax City draws its water from Goose Creek in Loudoun County. The city's system also serves 43,000 customers in parts of northwest Fairfax County, Herndon and Loudoun.

Berker said officials in Herndon and Loudoun also have been asked to impose the mandatory weekend ban on car washing and lawn watering, but it was uncertain yeaterday whether they would. Fairfax city residents convicted of the illegal use of water face up to $100 fines.