An anti-tax group is opposing the bond issues totaling $325 million on Tuesday's ballot, saying that the interest costs of borrowing the money would add millions of dollars to the county's debt.

Arthur G. Purves, president of the Fairfax County Taxpayers Alliance, said the county government should not sell new bonds until the debt on the old ones is paid off. Purves said he was urging residents to vote against the four bond issues for human services, parks, transportation and libraries.

The alliance describes itself as a nonprofit, nonpartisan, volunteer organization founded in 1956 "to prevent excessive real estate tax increases."

The 200-member group is governed by a 21-member board. It is aligned with a group called Landowners Opposing Wasteful Expenditures on Rail, which is against the transportation bond sale because group leaders said too much of the money would go to Metro instead of roads.

According to Purves, the sale of $325 million in bonds would cost the county an additional $160 million in interest, or almost half the amount of the bond. This year, he said, the county will pay $234 million in debt service, or the cost of interest and principal on bonds already sold. This amounts to 16 cents of the county's real estate tax rate of $1.13 for each $100 of assessed value.

It is difficult to estimate the exact cost of the bond sales, county officials said, because interest rates fluctuate. Also, the county has a particular way of structuring the sales. Based on an interest rate of about 4 percent (the county's most recent bond sale was 3.54 percent), the cost of the proposed bond issues on Tuesday's ballot would be about $136.5 million over 20 years, said Len Wales, the county's debt manager.

Purves said the bond sales also would be risky because the county is not allowing for the possibility of a terrorist attack or natural disaster that could require Fairfax to borrow additional funds. "Each year the county borrows up to its limit," he said. "If we had a disaster such as an attack or hurricane, we have no borrowing reserve left."

Bond sales are limited to $200 million a year to protect Fairfax's AAA rating, the highest given by the rating services. County officials said the AAA rating saves the county money because the bonds sell at comparatively low interest rates. They believe the county government has proved it can manage its long-term debt successfully.

By law, the Board of Supervisors has to set the tax rate high enough to repay the bonds the county sells, which means there is little risk to investors, officials said. In periods when revenues drop, such as the 1992 recession, the county just stops borrowing money.

Instead of accumulating long-term debt, Purves said, the county should adopt "pay-as-you-go" financing, using the $234 million a year the county spends on debt service to build and repair facilities.

"Because the county is borrowing up to its limit [about $200 million a year], the amount they borrow is about the same as debt service [$234 million]," Purves said. "Each time they borrow, they owe another $100 million in interest. Wouldn't it make more sense to spend the money that is now spent on debt service on construction and not pay an extra $100 million a year in interest?"

County governments often choose to borrow money because the cost of capital projects usually exceeds available money, similar to a family taking out a loan to make a major purchase such as a car or a house addition.

If the county were to spend the $325 million from general funds instead of bond sales, debt manager Wales said, "we'd have to raise the tax rate accordingly" or deep cuts would have to be made to existing programs.

One cent of the tax rate brings in about $14.5 million, so the tax rate would have to go up about 22 cents on each $100 of assessed value to cover the $325 million in capital projects.

Supervisors have chosen to borrow the $325 million and spread the repayment costs over 20 years.