HARTFORD, Conn. – The race is on for more casinos in southern New England as Connecticut and Rhode Island look to expand to keep up with huge competition expected from Massachusetts’ entry into the business.

Connecticut’s Mohegan Sun is seeking to build a casino in Palmer, Mass., as other casino developers look at Springfield and Holyoke as competitors for a western Massachusetts site. And Rhode Island voters will be asked next year to approve a ballot question on whether to turn a slot parlor into a casino.

Massachusetts Gov. Deval Patrick signed legislation Tuesday authorizing the greatest expansion in gambling in the state since the lottery was established 40 years ago. The law authorizes up to three competitively bid casinos and one slots parlor. It caps a five-year effort that backers say will create thousands of jobs and generate hundreds of millions in revenue.

A slot parlor could be operating in two years, while it could be four years before destination resort-casinos are in business, said Massachusetts state Sen. Stephen Brewer, chairman of the Ways and Means Committee and a casino supporter.

Mitchell Etess, chief executive of the Mohegan Tribal Gaming Authority, which runs the Mohegan Sun in eastern Connecticut, praised Massachusetts’ foray into casino gambling. It’s a double-edged sword for the Mohegan Sun, competing with it while also giving it the opportunity to seek permission to build a casino in Palmer, Mass.

Connecticut government officials do not have dollar estimates related to the impact from new casinos to the north but expect competition to be “negative for Connecticut’s casinos,” Gian-Carl Casa, spokesman for the state Office of Policy and Management, wrote in an email.

Until details are available about the location, size and type of entertainment at casinos in Massachusetts, “we won’t know the magnitude,” he said.

Foxwoods and Mohegan Sun paid $342.3 million in slot machine contributions to Connecticut in the budget year that ended June 30. That was down 2 percent from the previous year due to competition from other states and the weak economy.

Casinos looking to open in the region do so at their own peril, said Connecticut state Sen. Eileen Daily, co-chairwoman of the legislature’s Finance, Revenue and Bonding Committee.

“There’s a limited amount to go around,” she said.

Rhode Island Gov. Lincoln Chafee said the state gets more than $300 million a year — the third-largest source of revenue — from its lottery and two casinos. State officials have commissioned an economic impact study of “various likely competitive threats” to the casinos, Twin River and Newport Grand.

Patti Doyle, the spokeswoman at Twin River, said casinos in Massachusetts could be a significant competitor if Rhode Islanders switch their allegiance to new casinos nearby.

To keep gamblers closer to home, Rhode Island will vote next year on a referendum that would allow table games and dealers at Twin River, which now offers slots.

“If that passes, then I think we have a very good shot at a level playing field,” she said.

The Massachusetts law calls for spreading the casinos across different regions, with one each in eastern Massachusetts, western Massachusetts and the southeastern part of the state.