PLAINVILLE — Earth-moving machines and hard-hat workers crawl over the grounds of Plainridge Racecourse, busily building a 1,000-car parking garage that the flagging racing industry could not possibly fill.

For the partnership that owns the racetrack, the $20.5 million garage is a featured element in their application for the state’s sole slot parlor license. The harness racing track, at Route 1 and Interstate 495 near the Rhode Island border, will make a case that its development proposal is the furthest along — in planning, design, permitting, and construction — and would be the quickest project to open and to produce tax revenue if awarded the license.

“We took a $20.5 million gamble,” said Plainridge president Gary T. Piontkowski.

For the gamble to pay off, the track will need to beat some new competitors for the license, which have begun to emerge as the state’s Jan. 15 application deadline approaches.

A 15-minute drive down Route 495 from Plainridge, Raynham Park owner George Carney has struck a partnership with Greenwood Racing, owner of Parx Casino & Racing in suburban Philadelphia, to pursue a slot parlor license at the simulcast parlor and former dog racing track in Raynham.

“We could have gone anywhere in the state,” said Greenwood chief executive Tony Ricci, “but this is the best location.”

More competition for the license is possible in Littleton, Charlton, and perhaps other communities.

The state’s 2011 gambling law authorizes up to three resort casinos, each costing at least $500 million. The resorts will pay a 25 percent state tax on gambling revenue. The law also creates a license for one slot parlor, limited to 1,250 machines and no table games.

The law sets a minimum initial investment of $125 million for the slot parlor, and requires the facility to pay higher taxes: 49 percent of gambling revenue.

The state gambling commission controls the casino licenses and will award them through a competition. The commission hopes to issue the slots license in 2013.

As of Friday, Plainridge was the only contender for the slots license to have paid its nonrefundable $400,000 application fee.

In a recent interview at the Plainville track, Piontkowski showed plans, permitting documents, and architectural drawings for the project, developed during the past several years, which he said puts Plainridge far ahead of any other competitor.

“We’re picking the colors for the bathrooms,” Piontkowski said.

Should Plainridge not win the license, the track would have a new parking garage it doesn’t need for the racing business. More notably, there would be no racing business — Piontkowski said the track will not survive without slots, and the owners would need to market the property for some other use.

At Raynham, Ricci said his company liked Carney’s property in part because it is close to Boston and has been a gambling operation for many years.

“Many of the people in the community either work there or patronize the place,” he said. “You’re accepted from the beginning.”

Ricci also likes his firm’s new partnership with Carney, who has been in the Massachusetts racing business for decades.

“We could have opted to go it alone in another area, but we felt having someone of George’s reputation and experience and relationships in the community would make it a much better enterprise than we could do alone,” Ricci said. “We think that we have the best possible situation where we have the financial strength and the operational experience, with a guy who intimately knows this market.”

Another potential slots developer, Clairvest, a Canadian private equity firm, confirms it is interested in developing a slot parlor in Littleton.

“Given Clairvest’s focus on the gaming industry across North America, we are currently evaluating the potential for a [slots parlor] gaming license application in the town of Littleton,” the company said in a statement to the Globe. “Specifically, we believe ‘The Point’ development currently underway at I-495 and Great Road has the potential to be the ideal location.”

Clairvest is considering a roughly 100,000 square-foot development. “At this time, Clairvest is only evaluating the potential for such a development, and has not submitted a formal application to the commonwealth or a proposal to the Town of Littleton.”

Clairvest promised “a transparent process” if it submits an application.

And businessman Vincent Iuliano, who controls a site on the Massachusetts Turnpike in Charlton, said a number of gambling firms have visited the property, which he said is ideally located to intercept Massachusetts residents heading to the Connecticut tribal casinos.

“We’re not going to affect any [resort] casino market in Massachusetts,” he said. “The only thing we’re going to do is cut off money going to Connecticut.”