Under terms negotiated by Mayor Giuliani, the city has forgone almost $27 million in rent from its two Major League Baseball teams in the past four years to subsidize their efforts to plan and design new stadiums, and the teams will be able to reduce their rent payments by a total of up to $30 million for stadium planning in the next three years.

Although Mayor Bloomberg announced with great fanfare this week that he had reached deals with both the Mets and the Yankees to help finance the infrastructure for those new sports venues, a key provision of the teams’ lease agreements with the city went unmentioned.

Both teams have been eligible for annual rent deductions of up to $5 million as incentives to build, or at least study the possibility of, new stadiums.

The Mets reduced their rent payments to the city by a combined $15.95 million spent on planning costs between 2001 and 2004, while the Yankees shaved their rent bills by $10.97 million, according to the city’s Department of Parks and Recreation, which oversees the leases.

That comes on top of the new commitments the city has made to help finance the infrastructure for both stadiums.

It plans to earmark $135 million in the Bronx for the replacement of the “House That Ruth Built” and $85 million for the Mets in Flushing.

Yet even with the discounts and with additional investments by state government, the taxpayers will probably end up paying less for those stadiums than taxpayers have for baseball stadiums in several other cities. They will certainly be paying less under these agreements than they would have for the proposed West Side stadium for the Jets, which failed to win approval from a state board last week.

On Sunday, when Mr. Bloomberg announced that his administration reached a deal to build a new Mets stadium and to preserve in modified form the city’s Olympic bid, he said the work was accomplished during a 72-hour negotiating marathon. While the fine points and the expansion of the new ballpark for the Olympics were hammered out during those sessions, the city’s involvement in both planned stadiums dates back years, as evidenced in its leases.

The chairman and chief operating officer of the Mets, Fred Wilpon, said Sunday that the research and environmental studies the organization conducted in the past few years were crucial to the speed with which it was able to strike a deal with the mayor.

Both teams’ lease agreements were set to expire this year, but the teams each have five one-year renewal options, according to an audit report issued last December by the comptroller. A Bloomberg spokesman, Jordan Barowitz, said yesterday that both teams will continue to be eligible for the rent reductions of up to $5 million a year for the next three years, while they plan the construction of their stadiums. Both facilities are to open for the 2009 baseball season.

Meanwhile, the city comptroller, William Thompson Jr., has been conducting an audit to ensure that the Mets have complied with the lease agreement. The audit, which is routine, was requested by the Parks Department.

In his last audit of the Mets, released in June 2003, Mr. Thompson found that the team owed the city $4.56 million for underreporting its revenue, overstating allowable rent deductions and credits, and failing to remit $3.3 million in back payments that it owed the city as a result of previous audits. The team paid the city $590,113 before that audit was complete and later settled with the city’s Law Department for $2.75 million.

A spokesman for Mr. Thompson, Jeff Simmons, said such audits are a way of ensuring that private businesses operating on city-owned property “comply with the terms of their agreements, properly report revenues, and pay the city all fees due.”

The Mets have paid the city $24.5 million in rent over the last five years, but the city has paid $20.8 million for maintenance costs at Shea Stadium. The city will no longer be responsible for those costs when the new stadium is built. The city also collected $17.7 million in parking fees from Shea. At Yankee Stadium the city has collected $26.4 million in rent.

The lease agreements have been a source of controversy for years. On his way out of office, Mr. Giuliani amended the city’s leases with both the Mets and the Yankees.

According to published reports, the changes to the Mets lease relieved the team from paying the city percentages of revenues earned from the advertisements behind home plate, which the team long argued it should not have to turn over to city coffers, and from paying for certain aspects of its licensing revenues for broadcasts. The amendments to the Yankees lease included a clause that would allow the team to terminate its lease with only 60 days’ notice.

Three years ago, Mr. Thompson criticized Mr. Giuliani’s lease amendments and said the agreements had “certain troubling provisions.” He called on Mr. Bloomberg to renegotiate the deals to “protect the city’s financial interests.”