Marylanders left the state to spend about $1.2 billion at the Hollywood Casino in Charles Town, W.Va., over the past decade, money they could have pumped into the local economy instead, according to a report released Monday by a group that wants to expand casino gambling in Maryland.

The study, conducted by the Sage Policy Group and funded by supporters of gambling expansion, makes an economic case for building a new casino at National Harbor and allowing table games elsewhere in Maryland, something the state's voters would have to approve Nov. 6.

Unless gambling is expanded, said Anirban Basu, Sage Policy Group's chairman and CEO, "Marylanders will spend between $1.1 billion and 1.5 billion in Charles Town over the next decade."

Basu said table games at Charles Town, which opened in late 2009, cut particularly deep into potential Maryland revenue. Charles Town's revenues jumped from about $400 million to about $570 million since the table games opened, the report showed.

"The competition is not on a level playing field," Basu said. "Charles Town offers table games, Maryland does not."

A new casino in Prince George's County could also help break Marylanders of the habit of traveling to West Virginia to gamble, Basu said. Not only would the casino draw from Montgomery County, but it could attract gamblers from Northern Virginia as well, he said.

"You can find slot machines in other states," Basu said. "Our facilities have not been good enough or different enough to attract more out-of-staters."

Gambling opponent Arthur Turner, president of the Coalition of Central Prince George's County Community Organizations, said any study funded by supporters of gambling expansion can't be trusted.

"Whenever someone pays you, you skew your research to support whoever's writing the check," Turner said. "Those people are not truthful."

He noted that the report didn't take into account the greater availability of Maryland casinos or the social ills wrought by gambling.

"At some point there's market saturation," Turner said. "When do you stop and say, 'Enough'?"

Prince George's County estimates that it would take in $41.4 million a year in tax revenue from a new casino, including property taxes, income taxes and other taxes on gambling, hotel rooms and other amusements. The casino would also boost nearby businesses, said Brad Frome, deputy chief of staff to County Executive Rushern Baker.

Sage Policy Group's report is the latest salvo in an all-out fight over the expansion of gambling in Maryland. An independent poll from Gonzales Research & Marketing Strategies released late last month found that 46 percent of Maryland voters oppose an expansion of gambling while nearly 45 percent support it -- a statistically insignificant margin.