ALBANY - Gov. Eliot Spitzer and legislative leaders agreed Thursday to reform a pro-union, anti-corruption mandate that officials have long blamed for driving up publicly paid construction costs.

The reform of the 1921 Wicks Law has been an elusive goal in Albany for years, but the agreement announced Thursday would exempt more than half of public projects from the mandate.

Under Wicks, municipalities and school districts must separately bid most construction projects.

That means they must draw up specifications, solicit bidders and award separate contracts for plumbing, heating, electrical and other elements of public construction.

The law now applies to publicly financed projects that total more than $50,000, a level set in the 1960s, which applied to almost all public projects.

The Buffalo Niagara Partnership and other business groups seeking lower taxes have estimated Wicks drives up the cost of public construction by as much as 30 percent.

By comparison, private-sector jobs usually include a general contractor who can cut costs in choosing his or her own subcontractors, which can result in the hiring of fewer construction workers and other savings.

“It was a significant step forward - 43 years and we have reform,” Spitzer said.

Trade unions have long opposed a substantial easing of Wicks. Spitzer had sought greater reform of the mandate as a way to reduce costs paid by taxpayers, but said Thursday's deal will still cover more than 70 percent of public projects.

Labor unions would still benefit from the biggest contracts.

The differences reflect the geographic differences in construction costs.

The agreement means the law won't be required for public projects totaling less than $3 million in New York City, won't apply to projects worth less than $1.5 million in the New York City suburbs; and won't apply to upstate projects worth less than $500,000.