Just as Maryland's political leaders were digesting the news that slot machines could soon be arriving along the state's northern boundary in Pennsylvania, word came last week that gambling interests were beginning a push for slots to Maryland's south.

A District businessman acknowledged that he had plans to build a gambling parlor with 3,500 slot machines in Northeast Washington, a few miles from the Maryland border, and had filed a request with the D.C. Board of Elections and Ethics to put the matter before voters in November.

That was sobering news to opponents of slots in Maryland who had just taken a field trip to Harrisburg, Pa., to motivate the handful of lawmakers there who are fighting a slots proposal put forward by Gov. Edward G. Rendell (D).

Del. Peter Franchot (D-Montgomery), one of the people behind the anti-slots movement in Maryland, said he learned of the D.C. effort during a conversation with aides to Mayor Anthony A. Williams (D).

Franchot said he was and still is trying to help organize a group of political leaders from the District, Maryland and Virginia "in case Pennsylvania falls," to create a firewall to stop the spread of slot machine gambling across the mid-Atlantic.

Franchot said he has support from Rep. Frank R. Wolf (R-Va.), a longtime gambling opponent, to host a regional meeting on the subject.

"The gambling industry in this area is thick as cicadas," Franchot said. "The problem is they don't go away for 17 years. So it's constant vigilance. You can defend your state, but it has to be round-the-clock."

Gov. Robert L. Ehrlich Jr. (R) said he was surprised by the D.C. slots effort and that he saw little about it that would serve the interest of Marylanders.

"It's just another venue for adults in Maryland to travel to spend their discretionary income," Ehrlich said.

"But clearly it creates more political pressure" on Maryland to legalize slot machines, Ehrlich said. "The more states that fall into that category, the more pressure there is on us to act."

One interesting aspect of the D.C. proposal is how small the city's cut would be, several lobbyists and lawmakers said this week.

If approved by voters, the D.C. slots operation is likely to generate about $400 million a year in profits, although gambling analysts have said it could be twice that. Just a quarter of the money would go to the District, as a tax earmarked for public schools, prescription drugs and other services. The developer of the slots initiative would keep the rest, making it one of the most lucrative deals for a private slots operator in the nation, gambling analysts said.

"Every other proposal I've seen gives more money back to the public," said lobbyist Gerard E. Evans, who represents the Maryland Thoroughbred Horsemen's Association. "To me, it shows what a great deal it is in Maryland the way the bill came out of the Senate."

The gambling plan Maryland lawmakers rejected last month would have given the state nearly 50 percent of slots proceeds. Other states collect up to 80 percent of slots profits, said Jeff Hooke, a Virginia investment banker who has studied gambling initiatives across the country.

Staff writer Lori Montgomery contributed to this report.