The measure, which is on the November ballot, would allow some 15,000 slot machines at five locations in the state, including in Anne Arundel County. During the news conference held at Calvary United Methodist Church, the organization brought forth church and civil rights groups, unions and Maryland Comptroller Peter Franchot.

Gov. Martin O'Malley, talking to reporters before the anti-slots kickoff, groused about Mr. Franchot's vocal opposition to slots.

"The comptroller has had the wonderful luxury of sitting back and doing nothing to help us restore fiscal responsibility while throwing stones (at the slots proposal) in a hypocritical way," Mr. O'Malley said. "He's not at all ever troubled by his inherent contradictions, and he never saw two sides of an issue that he couldn't be simultaneously in favor of."

Mr. Franchot supported slots several years ago when he was a delegate in the legislature. His spokesman, Joseph Shapiro, fired back a volley later in the day.

"It is highly unusual for a sitting governor to attack another statewide official, especially a member of his own party. However, that is exactly what Gov. O'Malley did today, and it is regrettable," he said in a written statement.

"The effort to legalize slot-machine gambling, which the governor himself fought to place on the ballot, began in earnest today," Mr. Shapiro continued. "Comptroller Franchot ... is strongly opposed to amending our constitution, saddling Marylanders with another tax and undermining the fiscal integrity of our State."

At the Marylanders United event in Annapolis, Mr. Franchot said voters should reject false choices offered by slots supporters.

"They will come in and say, 'Vote for this or we will have to raise taxes, or cut services,' " he said. "Consider the source. This fact is indisputable: The same folks who are pushing slots just passed through the largest tax increase in state history."

He said the slots measure amounts to a regressive tax on those already hurting.

"Slots won't lower your taxes," said Hilary Spence, treasurer of Marylanders United to Stop Slots and a former Talbot County councilwoman.

Barbara Knickelbein, co-chairman of NOcasiNo Maryland said money that might otherwise move through the state's economy will be sucked up by slots.

"To generate $600 million in revenues, $1 billion will have to be lost by people who can't afford it," she said. "The only way for Maryland to win is for Marylanders to lose."

She and other speakers acknowledged the challenge in front of them. With most state leaders, several unions, the Maryland Association of Counties and powerful gambling interests backing the bill, it will be an uphill battle to thwart slots.

"It's the 800-pound gorilla, that probably weighs even more now," Ms. Knickelbein said.

When Mr. O'Malley and legislators ironed out fixes for the state's structural deficit during the special session last year, slots income became part of the long-term solution.

Yesterday, Mr. O'Malley underscored the need for that income.

"Hopefully, the opponents have a suggestion as to where else the people of Maryland, the state of Maryland, will get these important dollars that are currently building schools and addressing public needs in Pennsylvania, Delaware and West Virginia," he said, citing neighboring states where slot machines are in place.

But opponents argue that becoming dependent on gambling revenue to solve short-term budget problems and maintain the state's quality of life will lead to even more gambling when another budget crisis hits.

"What happens when the slots revenue is lower than expected; do we try casinos?" Ms. Knickelbein said. "Does Ocean City become Atlantic City south?"

Marylanders United to Stop Slots released a list of 100 people serving on the coalition's steering committee. One of them is County Councilman Josh Cohen, who underscored the gambling expansion worry.

"Slots is just a lousy way to fund government services," he said. "The big concern is if the state becomes dependent on billions in slots revenue the state will have a vested interest in protecting that revenue and increasing it.

When neighboring states expand slots to full-fledged casinos in order to get bigger, there will be pressure on Maryland to do the same, he said. "It is a very slippery slope."

Polls indicate voter support for slots slips when they discover that allowing slots requires a constitutional amendment, and Marylanders United is pressing that point.

The coalition yesterday also launched an Internet advertisement urging voters to "Say no to amending the constitution to bring slots in Maryland."

Aaron Meisner, chairman of StopSlotsMaryland, warned if the amendment is approved, and the slots experiment goes awry, it would take a super majority - 3/5 of the legislature - to change it.

"Like the U.S. Constitution, the Maryland Constitution is difficult to amend," he said. "It is made to derail marginal ideas."

"It is bad enough to let these predators into Maryland without letting them into the Constitution as well."

Bishop John R. Schol, head of the Baltimore-Washington conference of the United Methodist Church, was one of three church leaders on hand. He said the leaders of 700 congregations have signed on to stop slots.

"At all these churches we will be teaching, preaching, and working to defeat slots," he said.

After offering an opening prayer, the Rev. Bryan Brought, pastor of Calvary United Methodist Church, which hosted the campaign kickoff, told a story he said underscores the reason for his stand on slots.

A parishioner told the Rev. Brought he had seen a woman at the drug store across from the church who was in line to make a purchase and buy a lottery ticket.

"But she did not have enough money for both," the Rev. Brought said. "So she bought her scratch-off lottery tickets. And she walked away leaving the item she was going to purchase at the counter.

What she was going to buy was a bottle of children's cough medicine."

The Associated Press contributed to this story.