A tentative deal to change Maryland’s law on dog bite liability is close to unraveling in the General Assembly.

Last month, the House of Delegates unanimously passed a bill to address a Maryland Court of Appeals decision that declared pit bulls “inherently dangerous” and automatically held their owners responsible if they bit someone.

The House bill removed from the law the breed-specific language that singled out pit bulls and shifted the burden of proof in dog-bite cases to the owner rather than the victim.

At the time, it appeared the Senate was on board too. The bill was the product of negotiations between leading members from both chambers.

But it seemed clear Tuesday that the deal wasn’t holding up. The Senate took up a separate version of the bill that included a new provision making it more difficult for dog owners to prevail in lawsuits. To do so, they would have to provide “clear and convincing” evidence that their dog was not dangerous before the attack.

“It makes it virtually impossible for a defendant to prevail,” said an angry Del. Luiz Simmons (D- Montgomery), the House negotiator on the bill.

Simmons said he felt betrayed by Sen. Brian E. Frosh (D-Montgomery), who negotiated the bill for the Senate.

“He told me he agreed with the compromise, he told me not to worry about it,” Simmons said. “We had a deal.”

Frosh, chairman of the Senate Judicial Proceedings Committee, said that he was in “an awkward position” but that events had taken an unforeseen turn.

The new provision was proposed last week by Sen. Robert A. Zirkin (D-Montgomery) and approved by a majority of members of Frosh’s committee, with Frosh voting against it. Still, Frosh said he didn’t think Zirkin’s amendment hurt the bill.

After the bill arrived on the Senate floor Tuesday, Minority Leader E.J. Pipkin (R- Cecil) unsuccessfully tried to delete Zirkin’s provision.

“I love dogs but if my dog bites a little kid, I should be responsible,” Zirkin said as he spoke in defense of his measure.

Sen. Delores G. Kelley (D-Baltimore County) also spoke up in favor of strict liability for dog owners.

“I am a victim of a dog bite,” she said. “I was four years old when I was bitten by a German Shepherd on the buttock. ... You may not see the scar, but emotionally it has affected me for the rest of my life.”

The future of the legislation is now uncertain. What’s clear is Simmons is very upset.

“This is about Chairman Frosh getting cold feet and getting wobbly with the trial lawyers,” Simmons said. “This isn’t about Zirkin, it’s Frosh’s committee. He decided he could have it both ways, he could say he’s for the compromise, he’ll speak against the amendment, but he won’t lift a finger to stop it.”

Members of the General Assembly have struggled over the past year to craft legislation that would address last year’ s court decision in which owners of pit bulls (and “third parties,” including landlords) became automatically liable in the event that their dog bites or injures someone.

In a special legislative session last summer, members failed to reach a compromise. If they don’t do so in the remaining days of the regular session, the court decision declaring pit bulls “inherently dangerous” will stand.

The court decision, Tracey v. Solesky, arose out of a 2007 incident in which a pit bull mauled a 10-year-old Towson boy.