THE PROMISE of slot machine gambling was so wildly oversold to Maryland voters, who approved it three years ago, that it’s a wonder the General Assembly in Annapolis is not targeted daily by protesters demanding to know what happened to the money.

Originally, state budget analysts predicted that slots revenue would yield $76 million for education in fiscal 2011, and nearly $500 million in the current fiscal year. The actual take last year was scarcely two-thirds the amount projected and will probably be less than a fifth the amount forecast for this year.

Even after the scheduled opening this summer of what will be the biggest gambling parlor in Maryland, and one of the biggest in the United States — a 4,750-slot-machine colossus in Anne Arundel County — officials say the state’s take from gambling over the next five years will be 12 percent less than expected: a shortfall of some $475 million.

So Maryland residents can be forgiven if they’re skeptical about the hype surrounding the latest supposed windfall, from a proposed expansion of gambling now under consideration by state lawmakers. Under a bill that sailed through the state Senate last week, voters would be asked to approve a sixth casino — this one in Prince George’s County — as well as table games, such as blackjack and roulette, for all gambling venues in the state. And just in case all that doesn’t translate into sufficiently fat profits for the casino operators, Maryland would also sweeten the pot by cutting its share of the proceeds by more than 20 percent.

We have long opposed gaming in Maryland because of the social ills that accompany it, such as gambling addiction, and because it is often tantamount to a voluntary tax on the poor and the vulnerable. In a time of economic stress, those arguments seem stronger than ever.

But it seems equally valid to oppose an expansion of gambling on the basis of the fraudulent assurances with which slots were sold originally. Why be fooled twice?

Perhaps with that in mind, a growing number of lawmakers in Prince George’s are coming around to the view that, if there is to be a casino in their county, it should be one whose victims — er, customers — are mostly well-heeled fun-seekers from the District, Virginia and farther-flung locales.

That is central to the proposal pushed by Rushern L. Baker III (D), the Prince George’s county executive, who wants a $1 billion gambling palace built at National Harbor, the shopping, hotel and residential development just south of the Beltway. A casino of that scale and glitz — Las Vegas on the Potomac — built at private expense in a venue that already attracts many out-of-towners, would not draw most of its clientele from Prince George’s. Or so the argument goes.

Mr. Baker, a longtime opponent of gambling, flipped under intense pressure from the state Senate president, Thomas V. Mike Miller (D-Calvert). Mr. Miller wants a casino in Prince George’s and says, outrageously, that without one the county will not get the funds it needs to build a new hospital, which Mr. Baker badly wants.

Perhaps Mr. Baker sees his proposal as the least bad option available to him — that if Prince George’s must have a casino to satisfy a political force majeure, it should at least be a first-class facility that preys primarily on out-of-staters, not locals.

Fine. But this time voters should not be fooled into thinking that an expansion of gambling is a good idea, let alone a panacea for Maryland’s perennial problems in balancing its budget and funding its schools.