The Colonial Pipeline Co. will be asked to pay about $800,000 to cover local, state and federal costs incurred in last month's pipeline spill in Northern Virginia, according to preliminary estimates.

The spill March 6 dumped about 300,000 gallons of kerosene near Manassas, threatening the Occoquan Reservoir, drinking water source for 600,000 persons, and 63,00 gallons of home heating oil flowed into the Rappahannock River and imperiled the water supply of Fredericksburg, Va. Officials indicated yesterday that the cleanup costs could be more than the estimates.

Colonial Pipeline spokesman Wil Nicoll said the company has insurance that will pay "a majority of the costs. But there is a large deductable that the company will assume. We don't have total estimate, but feel that it will probably be several hundred thousands dollars."

The company has assumed responsibility for the cleanup costs. It could also be fined an undertermined amount if the U.S. Environmental Protection Agency decides to bring charges that the company failed to promptly notify officials. The Fredericksburg spill went undetected for several hours and officials apparently were not notified for about 24 hours after it occurred.

The spills occurred when an unmanned pumping station at Conowingo, Md., unexpectedly shut down, causing a massive pressure buildup along the northern section of the firm's 1,500-mile pipeline. Colonial officials said human error was responsible for the failure to relieve the pressure before the breaks occurred.

Calling the situation "a hell of a mess and a costly spill," Thomas Schwarberg of the Virginia State Water Control Board said, "we will have to get $126,000 to supply the Occoquan Monitoring Lab, the Virginia Institute of Marine Science and Mary Washington College with funds just so they can do their environmental assessment."

The largest claim apparently will come from Fredericksburg, where Assistant City Manager Peter kolakowski said it will total between $221,000 and $250,000. The state health department has ordered the city to continue purity tests and activated carbon treatment of water from the Rappahannock River, which supplies about 50,000 residents of that area.

Unofficial estimates of federal cleanup costs are between $175,000 and $200,000 for "manpower, equipment and materials," according to the Environmental Protection Agency's regional office.

The Fairfax County Water Authority will seek reimbursement of $160,000, "90 percent of which is for chemical and activated carbon costs," according to James Warfield, the authority's public information officer.

Other claims are expected from Fairfax County ($6,381.60 for cleanup expenses), Stafford and Spotsylvania counties ($18,000 to $23,000) and the Prince William County Fire Department ($16,000).

The Northern Virginia Regional Park Authority plans claims that apparantly will reach $65,000. It has decided to close Bull Run Marina, where the major kerosene recovery effort took place, for the reest of the year. wThe marina's banks remain "smelly and foulded," according to spokeswoman Dorthy Werner.

Robert Brooks, a lawyer with the Richmond firm of Hunton and Williams, representing Colonial, said some settlement checks will be sent to Fredericksburg business as early as next week.