GOV. MARTIN O’MALLEY has frequently complained that gambling is the tail that wags the dog in Maryland politics. As if to prove the point, he is now summoning state lawmakers to Annapolis, interrupting untold numbers of summer vacations, for a special legislative session devoted to adding a sixth casino to the five already authorized in the state, allowing table games like roulette in existing slots parlors and permitting gambling venues to stay open round-the-clock.

So how much does the state stand to gain from all this? Maybe $200 million a year, at a generous estimate, five or so years from now. That’s just a little more than 1 percent of Maryland’s annual general fund revenue.

The governor is within his rights to sound petulant at so much effort being expended to produce so little benefit. (“I’m so sick of this issue,” he told reporters Wednesday. “I just want to get it behind us.”) But to his credit, he has produced a blueprint for expanding gambling that, while not exactly inspirational, might be workable.

Mr. O’Malley’s plan, which, if passed by the General Assembly, would be presented to voters at referendum in November, would give a green light for a Las Vegas-style mega-casino, with 3,000 video slots plus table games, in Prince George’s County. In an attempt to muffle bitter complaints from existing casino operators who hate the idea of more competition, the legislation would sweeten the pot for everyone — not only by allowing table games and longer hours but also by cutting taxes by up to 17 percent for big established casinos.

Maryland’s gambling program, approved by voters in 2008, was oversold from the outset, which is one reason we opposed it then. Five casinos were authorized, of which just three have so far opened. Revenue projections were overstated, as was the promise that the tax income would repair the state’s structural deficit, fix schools and rescue moribund horse tracks.

Similarly, it won’t be a surprise if the governor’s newest projections — that his plan would add $200 million to current revenue estimates — are also inflated. Still, the reality is that three of the four states surrounding Maryland have robust gambling programs, and lawmakers in Annapolis still face projected budget deficits. The state needs money. If the governor’s plan or something similar is enacted and approved by voters, the state’s gambling program could eventually yield $500 million to $800 million annually for Maryland schools.

Mr. O’Malley’s plan has a number of other attractive features. One is that it would limit the gambling industry’s influence in state politics by banning contributions by casino companies and their executives to state and local candidates. If that’s doable, and passes constitutional muster — two big ifs — it’s a good idea. The bill would also shift some of the exorbitant cost of buying and leasing slot machines to casino operators from the state, which has already spent more than $250 million on them.

We wish we could be as optimistic as Mr. O’Malley that his bill would at last remove gambling from the state’s political agenda, which it has dominated, or at least complicated, for the better part of a decade. But deep-pocketed gaming companies have proved an exceptionally tenacious lobby. Whatever the outcome of this special session, we doubt they’ll be quiescent for long.