The assessed value of the average home in Prince William County is expected to increase by 35 percent this year, but county officials say a severe tax cut will spare the taxpayer a greater financial burden.

"The tax rate has got to come down," said Board of Supervisors Chairman Kathleen Seefeldt.

Prince William County is in the process of complying with a 1975 state law requiring all jurisdictions to base real estate assessments on 100 percent of the market value.

The last reassessment in Prince William was in 1974, and "that is the reason for the rapid rise people will see in their tax bills," said Paul Shegogue, acting finance director for the county.

Homes currently are assessed at 33 percent of their value and taxed at a rate of $5.25 for each $100 of assessed valued. County officials note that under the current system, the average home in the county is assesed at $45,000 making the average tax bill $767. The same home on today's market, Shegogue said, is valued at $60,000.

In April, the county Board of Supervisors will consider a new real estate tax rate after the school board and the county executive submit their budgets for fiscal year 1981 to the supervisors.

Shegogue says he expects the supervisors to reduce the tax rate to $1.30 per $100 of assessed value, in an effort to keep 1980 tax bills on a par with last year's.

Board Chairman Seefeldt said she is not sure what rate the board will set, although she, too, expects the rate to be lowered. "I have heard everything from $1.30 to $1.13," she said.

Seefeldt said that, even with a rate decrease, county residents may see slight increases in their tax bills after the adjustment is made to bring the county in line with the 100 percent assessment.

"Even if taxes went up a little, Prince William would be a far cheaper place to live than in other places in Northern Virginia," she said.

In neighboring Fairfax County, the real estate tax rate is $1.53 per $100 of assessed value.

Contrary to the past, Shegogue said every home in the county is being "individually inspected." To help in the reassessment, he said, the county has purchased a new computer-assisted system and hired more assessors to handle the workload.

In March, Shegogue said, the finance office will begin a countywide mail-out informing taxpayers of the change in assessment ratio. County residents can expect to receive their tax bills in June, he added.

In Prince William, residents can pay their yearly taxes in two installments, on July 15 and Dec. 2. At least 50 percent of the total bill must be paid in the first installment, Shegogue said, or a 10 percent penalty will be charged.

In 1979, the county collected $33,642,346 in real estate revenues, excluding delinquent payments, Shegogue said.