Boston Mayor Martin J. Walsh has backed down and OK’d the sale of IndyCar tickets despite promoters still lacking a single permit from the city and state to turn the Seaport District into a noisy, high-speed race course.

Walsh last November had blocked Grand Prix of Boston from selling tickets to the Labor Day weekend event, saying they needed to get signed final approvals from the city and state.

But the mayor’s office said yesterday he was informed that Grand Prix of Boston would start selling tickets to the public next week, and a spokeswoman said he did not object.

It’s unclear why Walsh reversed himself, but race promoters have been under pressure from nervous investors to get the necessary permits to hold the race. That pressure led to the promoters, city and state signing an “intent” agreement last December.

Promoters have refused to disclose their investors but say they have enough financial backing to make the race a success.

Race officials yesterday said a final agreement was imminent. It’s at least the third time promoters have asserted that deals with Walsh and state agencies were imminent or close to being signed.

The Grand Prix group also asserted in December that tickets could go on sale before the end of the year, but three months later no agreements have been signed. The promoters also may need approval from environmental agencies to build the course over a contaminated waste site behind the Boston Convention & Exhibition Center.

A spokesman for the EPA did not return calls from the Herald for the past two days to answer questions about whether race promoters need to get permits from the federal agency.

Walsh personally brought the race to the city despite getting no input from Seaport District residents and he has staunchly defended it despite a series of stumbles and a change in leadership from the promoters.

Walsh’s original agreement with Grand Prix of Boston would have forced the city and state agencies to pay potentially hundreds of thousands of dollars for repaving and other street improvements. After being criticized for that deal, Walsh and promoters agreed to revoke it and now no public money will be used for the race.

A group of Seaport District residents have organized to oppose the race, saying they have concerns about the event creating major traffic problems in their neighborhood as well as race cars hurtling through the streets at up to 180 miles per hour.