The Maryland Senate signed off on Gov. Martin O’Malley’s proposal for a Prince George’s County casino Friday evening, capping a contentious day-long debate over its impact on the state’s five other gambling venues.

The Senate voted 28 to 14 to approve the governor’s bill, which also calls for table games at Maryland’s existing slots locations. Attention now shifts to the House of Delegates, where the plan has been a harder sell and leading lawmakers have signaled that they would make significant changes to the bill.

Supporters and opponents of a new casino promised to step up their lobbying efforts in the coming days, as a special session called by O’Malley (D) was certain to stretch into next week.

“I think we’re in good shape, but we have a couple of long days and long nights ahead,” said Prince George’s County Executive Rushern L. Baker III (D), a major supporter of a Las Vegas-style casino at National Harbor, who was in Annapolis on Friday.

Maryland voters would have to give their blessing to an expanded gambling plan in November.

The Senate also voted 41 to 1 for stronger liability standards for dog owners, an issue that has become a sideshow in the special session. Under the bill, Maryland would shed its status as a “free bite” state. Now, owners are often held responsible for a first attack only if the pet has a history of violence.

The measure, which the House is also considering, attempts to fix what many lawmakers viewed as a flawed decision this spring when Maryland’s highest court ruled that pit bulls are “inherently dangerous.” The designation made Maryland pit bull owners and landlords who own property where they are housed automatically liable for injuries.

The Senate bill would remove the dangerous designation from any breed and have Maryland, like most other states, consider owners responsible for any bite, including the first. Virginia and 13 other states still require victims to prove that an owner knew a dog had a propensity to be violent.

Marylanders might soon see more “Beware of Dog” signs that could limit a homeowner’s liability if someone enters private property and is bitten.

The Senate’s vote on the expanded gambling legislation followed more than four hours of debate on about two dozen amendments, most of which the chamber soundly rejected. Among them was a bid to scrap the Prince George’s casino and authorize only the table games, such as black jack and roulette, at the five slots locations Maryland voters approved in 2008.

Sen. James Brochin (D-Baltimore County), who proposed the amendment, argued that the revenue the state would reap from table games is “low-hanging fruit” and that a new casino could significantly hurt business at several existing locations.

That has been the argument of Maryland Live!, the state’s largest casino, which opened in June in Anne Arundel County and has the most to lose from new competition in Prince George’s.

The National Harbor development, on the Potomac River, has emerged as the most likely site for a Prince George’s casino, but the measure would invite bids from a swath of the county that also includes Rosecroft Raceway.

Sen. Richard S. Madaleno Jr. (D-Montgomery), a proponent of O’Malley’s plan, argued that a Prince George’s location is “a unique economic development opportunity” that would yield financial benefits for both the county and state.

“I agree that’s a great location, but we’re doing it at the detriment to the other five sites,” Sen. Allan H. Kittleman (R-Howard) said.

The amendment to scrap the Prince George’s site was defeated 33 to 9.

The chamber also turned back an effort to provide the same concessions to a casino in Cecil County that the legislation offers to the Anne Arundel location and one planned in Baltimore.

To compensate for the new competition in Prince George’s, those two locations would get to keep an additional 5 percent of slots revenue, up from 33 percent, and could ask a gaming commission for more. The bid to include Cecil failed 31 to 13.

Several other failed amendments attempted to steer part of the state’s gambling proceeds to programs other than education, the current beneficiary.

One proposal would have used the new money to roll back an income tax increase on six-figure earners passed in the spring. Others would have steered some funds to transportation and programs for people with disabilities.

“This is not a pot of gold that everyone can go to,” Sen. James N. Robey (D-Howard) said in fighting off one amendment.

The Senate also turned back a bid to strip a provision from the bill that bans campaign contributions from casino owners to candidates and political parties in Maryland.

“I think our constituents are concerned about the undue influence this industry might have on us,” Madaleno said in defending the provision.