The estimated 900,000 Washington-area residents with dental insurance face the prospect of paying a larger portion of their dental bills because rapidly rising fees for dentistry are racing beyond the limits allowed by many insurance policies.

The higher prices being charged lately by area dentists reflect the soaring prices for gold and silver, which are used for dental fillings, bridgework and X-rays.

The proportion of a dental bill covered by insurance varies from company to company and from policy to policy.

"Some policyholders definitely will be more affected than others," said James Stroker, a spokesman for Blue Cross. He said those with policies based on a fixed fee schedule -- a predetermined flat amount -- would be hardest hit. About 70 percent of his company's policies rely on the fixed fee system.

Increases in dental fees vary, but one example was offered by Dr. Joseph Salcetti, president of the District of Columbia Dental Society.

"I have had two increases since November and there may have to be another one," he said.

For a three-surface filling with silver amalgam, a typical patient in Dr. Salcetti's office now pays $45 instead of $35.

When that fee exceeds the amount covered by the patient's dental policy, the patient pays the difference.

Insurance officials suggested yesterday that policyholders avoid costly surprises estimate and then requesting the insurer to make a pretreatment ruling on how much of the fee will be covered. Many insurers have forms for just such purposes.

"Then, if you go back to the dentist and say the company won't pay more than a certain amount, you can set up a dialogue to discuss the fees," said Charles Mundy, coordinator of the Aetna federal employes insurance program, which offers dental benefits for children of employes, but not for the employes.

Another option open to the consumer at that point, Mundy said, would be to find a dentist whose fees are closer to the amount that the insurer is willing to cover.

"Pretreatment estimates are a good idea anytime -- but especially right now," he said.

About 30 percent of the U.S. population has dental insurance, according to surveys made by the Health Insurance Association of America, an industry group that collects insurance statistics.

Nearly all dental coverage is sold through group plans, rather than individual policies. Generally the dental insurance, when it is available, is offered through employer or union health plans.

Prudential, for example, insures about 140,000 people in the Washington area through about 50 employer plans, including workers for utilities, schools, computer services, newspapers, radio and television and union groups.

Blue Cross estimated that its dental program includes about 39,000 people in the Washington area.

Government workers who have dental insurance benefits are covered through a number of insurers, including Aetna.

Mundy said that federal workers with Aetna dental coverage probably will not be caught as short by dental price increases as policyholders with some other companies.

He said Aetna relies on a reimbursement system that is updated every three months to reflect increases in dental costs. The last update was Jan. 1. In addition, interim changes can be made during any three-month period if surveys of dental prices show a need for adjustment in benefits, Mundy said.

As a general rule, there are two ways dental insurance benefits may be computed. One relies on a fixed fee schedule, which pays a predetermined flat amount, regardless of what the dentist charges.

For example, if the schedule provides for a fee of $22 for a two-surface silver amalgam filling, the policyholder can not collect more than that, regardless of whether the dentist charges $22 or $25. If the dentist charged $20, the company would pay only $20.

About 70 percent of the dental policies issued through Blue Cross are tied to fee schedules. Typically, those fees reimburse the patient for 50 percent to 60 percent of the average dental charges. An average fee paid on a $20 job would be $10 to $12.

About one-third of the 140,000 individuals with Prudential dental coverage in the Washington area depend on fixed fees, according to Jack Wild, senior claims consultant.

Wild said that compensation provided by those schedules can be increased -- but premiums would go up proportionatetly.

A second way that dental benefits may be computed depends on a "customary fee" program, which is updated about once every three months to keep pace with dental fee changes. The policy with this provision generally pays 60 percent to 80 percent of the customary fee that dentists in a geographic area charge. Some also pay 100 percent of the customary fee, officials said.