NEW YORK (AP) - The agency that owns the World Trade Center site has formally approved a deal with a developer over how to help pay for two towers on the site.

The Port Authority of New York and New Jersey voted Thursday. It had reached a tentative deal last spring with developer Larry Silverstein.

Port Authority Executive Director Chris Ward says stakeholders will share the financial risk in an effort to protect limited public resources.

The deal calls for the Port Authority to put up $1 billion to help finance a 64-story building already under construction. The money would only be used if the building doesn't repay its debt.

The agency also has agreed to provide $600 million backup financing for a 71-story tower, if Silverstein finds tenants and raises $300 million in cash.