Erie County's sales tax projections - a major part of an already tight county budget - may be overly optimistic and could create a huge problem next year, according to a new study.

Comptroller Mark C. Poloncarz released a report this week outlining a litany of potential problems in the county's proposed 2007 budget and four-year financial plan, and at the top of the list is one of the county's primary sources of funding - the sales tax.

Poloncarz raises questions about County Executive Joel A. Giambra's estimate that sales tax revenues will increase 3.8 percent next year when the growth in those revenues has slowed considerably the past few months.

"It's an area of concern," Poloncarz said Friday. "If the revenues come in 1 or 2 percent below those projections, that's a big hit."

Tax projections are especially important this year as county lawmakers haggle over where to cut and where to add in a budget that in Poloncarz's words has "little margin for error."

Giambra expects the sales tax to generate $369 million next year, up from $355 million this year. If those projections are off, it could mean a big hole in the budget.

"It was kind of surprising to us," Budget Director James M. Hartman said of the recent dip in tax collections. "The sales tax had been doing so well, we're wondering why this happened."

When asked if Giambra will amend his projections, Hartman indicated his office is taking a second look at its numbers, but no decision has been made. Under the charter, only the county executive can alter revenue estimates during the budget process.

Poloncarz said Giambra's sales tax estimates are high but not outlandish enough to qualify as a "deal breaker."

He did, however, raise concerns about other aspects of the budget and short-term financial plan.

Like the county's control board, Poloncarz pointed out what he called a disturbing trend in Giambra's four-year plan: a practice of putting off the hard decisions until the next county executive takes office.

His study raises questions about why Giambra's plan suggests the county wait until 2008 to end sheriff's road patrols or adopt a managed attrition program for cutting the county's work force.

"It basically leaves the decision for the next administration," Poloncarz said.

The report concludes that Giambra's budget is balanced on paper but nevertheless contains several problem areas. They include:

• The potential loss of up to $8 million in revenue from the annual sale of county tax liens. The county may have to discontinue the sale because of accounting changes.

• About $5.7 million that the county claims it is owed by the Erie County Medical Center. The hospital doesn't agree, and the matter could be headed to the courts.

• Nearly $1 million that Giambra expects to get from housing jail inmates from other counties. Poloncarz said Giambra's budget anticipates a 100 percent increase in that revenue line.