Suffolk Downs, long the leading contender for casino development rights in Greater Boston, submitted its nonrefundable $400,000 application fee to the state gambling commission Friday and formally ­applied for a casino license.

“We begin this formal part of earning a license to develop a world-class destination resort at our 77-year-old racetrack with great enthusiasm and with the understanding that our project must set the standard for gaming development in Massachusetts,” said a statement from Richard Fields,principal owner of Suffolk Downs. “With our partners, Caesars ­Entertainment, we are committed to a proposal that will create more jobs, tourism benefits, and local economic development than any other project in the state.”

The commission began accept­ing applications Thursday, nine months after Massachusetts legalized casino gambling. The state’s 2011 casino law allows up to three resort-style casinos in the state, with no more than one in each of three regions. Suffolk Downs applied for the Greater Boston and Worcester license, according to the form the track filed with its application fee.

The applications are the first step of a long review process that will stretch into 2013, butthey mark a milestone in the state’s efforts to develop the ­casino industry. The initial appli­cation period will be open for months, probably at least until the end of the year. Only official applicants will have access to state agencies to begin discussing the permits required in any large-scale development.

In June, Suffolk Downs unveiled its detailed plans for a gambling resort at the track in East Boston and Revere. The plans include a hotel, restaurants, a gambling floor with slot machines and table games, ­retail shops, and an entertainment venue. Thoroughbred racing would continue at the track if Suffolk Downs wins the ­license. Caesars, the Las Vegas-based gambling giant, would run the casino and would hold a small ownership stake in the project.

Plainridge Racecourse, the harness track in Plainville, submitted $400,000 Thursday to become the state’s first casino license applicant. The track is pursuing the single slot ­machine parlor license authorized by the casino law.

The bulk of the application fee will go toward paying for the gambling commission’s inves­tigation of all applicants, which could begin later this year. In October, the commission is expected to release a highly detailed application form seeking information on the finances of each applicant and the background of key officers and employees. The commission can reject any company with a shaky balance sheet or with people of questionable character in key jobs.

“I really don’t expect anybody will be weeded out based on the names of the players that have shown interest,” said Clyde Barrow, a casino specialist at the University of Massachusetts, Dartmouth. Most of the companies exploring bids in the Bay State are common names in the casino industry.

Companies that pass the background check will be qualified to submit a detailed proposal describing the projects they want to build, so long as they earn the endorsement of the host community in a referendum. The commission ­expects to be ready to receive those proposals next year.

Chip Tuttle, chief operating officer of Suffolk Downs, said the track is having discussions with Boston and with Revere over the terms under which the communities would agree to host a gambling resort. The agreements are required under the law. The developer is ­expected to compensate the communities to help offset the effects of the project.

The track is hosting two community meetings later this month to discuss transportation and traffic with residents. Traffic is one of the biggest concerns cited by opponents of the casino project. Suffolk Downs will host Revere residents Aug. 21 and East Boston residents Aug. 23. Suffolk Downs will present some tweaks to its transportation plan, which it continues to refine, Tuttle said.