IBM Corp. agreed yesterday to pay as much as $200,000 to clean up a well near Manassas that was shut down last month after tests disclosed it contained unacceptable levels of a suspected cancer-causing chemical.

Officials at IBM, which has a large plant about a mile from the closed well, said the source of the chemical, tetrachloroethylene, has not yet been determined. The agreement, in which IBM will pay to filter water from the well, does not mean the company is responsible for the well's contamination, company officials said.

Last October, the Environmental Protection Agency cited the IBM plant as a "long-term, chronic threat to public health" because of spills or leaks of the same chemical in the early 1970s.

The agreement between IBM and the Prince William County Service Authority, which will also pay $21,000 toward the filtration plan, is only a temporary solution. The filtration is to get under way in March and last up to six months. Although the process would filter water pumped from the well, it would not stop the flow of the chemical into the well.

The well, closed since Jan. 7, is off Rte. 234 near the Manassas line. It had provided water to a densely populated area northwest of Manassas, including the communities of Sunnybrook Estates, Stonewall Acres, Loch Lomond, Irongate and Westgate.

There are 12 other wells providing water to more than 26,000 people in the western part of the county. All of those wells have passed water quality tests and can handle the area's water needs, county officials said.

Tetrachloroethylene, the chemical found in the well, is a common organic solvent used in dry cleaning, degreasing processes, pesticides and some household cleaners. IBM used the chemical to degrease electrical components at the plant between 1970 and 1975.

Tests of water taken from the well last November showed the level of tetrachloroethylene at 197 parts per billion. There are no federal standards regulating acceptable levels of the substance, but some jurisdictions consider 5 parts per billion to be an acceptable limit. Federal officials said the evidence linking the chemical to cancer is inconclusive.