As the city’s plans gel for Vanderbilt Ave. rezoning, the MTA has quietly reopened the bidding for the long-term lease on its headquarters block at 341-347 Madison Ave.

The site between E. 44th and 45th streets is being vacated and the winning bidder is expected to tear it down and put up a new skyscraper.

Developers have until Oct. 14 to amend their bids or submit new proposals, according to the Sept. 17 notice. The MTA sent out its original request for proposals in June 2013 and later extended its deadline to October 2013 while reopening it to new bidders. But once de Blasio was elected the major Midtown East rezoning was scrapped and since then, the MTA deal has been in a holding pattern.

Cushman & Wakefield is overseeing the bidding on behalf of the MTA. Reps for both declined to comment.

The agency is asking that new bids for the building be based on a floor area ratio (FAR) of between 24 and 30, or as much as 753,150 square feet. Right now zoning laws would allow 376,575 square feet.

There are also requirements to “support public circulation” in the area either on or off site, and the developer would have to meet “findings” with regard to the ground floor level, the massing and energy performance of the new building.

Additionally, landmark properties are expected to be able to transfer more air rights to the new structure, and any hotel within the new Vanderbilt Corridor would also need a special permit.

Steven Spinola, president of the Real Estate Board of New York, said the Vanderbilt zoning proposal should be certified by City Planning by the end of October. “Up until recently there was uncertainty as to what the city was doing. Hopefully, this will encourage people to take another look at this site.”