Two groups have accused the Suffolk County SPCA of failing in its core mission, claiming the agency often ignores allegations of animal abuse or is too slow to investigate.

The groups — Replace the Suffolk County SPCA and Enforce the Animal Laws in Suffolk County — accuse the agency’s leaders of being “afraid” to make arrests and seize animals for fear of being sued.

Some animal activists said they’ve repeatedly alerted the Suffolk Society for the Prevention of Cruelty to Animals to alleged abuse, ranging from dogs being chained outside around the clock to businesses selling sick puppies, only to find their concerns brushed aside.

“There are probably tens of thousands of animals suffering, and I think a lot of that is on them,” said Deborah Maffettone of West Babylon, who co-founded Replace the Suffolk County SPCA in April 2015. “They’re not showing the county that they will not tolerate it.”

The activists have been pursuing several options, from trying to convince police to take over all animal abuse complaints, to filing for another SPCA charter in Suffolk.

But Roy Gross, the SPCA’s longtime chief, said the critics are “clueless” about animal cruelty laws and stressed that arrests can’t be made without sufficient evidence. He cited several recent convictions and an insurance policy as proof that the SPCA is not timid about locking up animal abusers.

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“We’re doing a great job,” he said, adding that the largely volunteer agency investigates roughly 3,000 complaints a year.

Gross said it’s unfair to blame the SPCA for problems beyond its control, including plea bargains that result in “slap on the wrist” penalties.

“Shame on them,” Gross said of critics. “We’re the good guys.”

Each side points to some of the same cases in buttressing their arguments, including Precious Pups, a Calverton-based outfit that was shut down by the state last year after about 50 people had complained that they were sold sick dogs, some of which had to be euthanized.

Maffettone said she had to gather dozens of initial complaints for state prosecutors to start a probe in 2014, two years after she notified the SPCA. Gross said the investigation simply took time, and noted that his agency collected much of the evidence used in the case.

Gross also cited the case of Robert Barrett of Yaphank, an Angora cat breeder who was charged with dozens of counts of animal neglect in September 2014 and who pleaded guilty Monday to one misdemeanor count of animal cruelty. Critics say cats suffered because Barrett’s arrest took too long — three years after a medical emergency at his home prompted Brookhaven Town and the SPCA to seize about 40 of his cats.

The national SPCA issues only one charter per county, but Enforce the Animal Laws is looking into whether it can apply for one in Suffolk.

On Friday night, Maffettone and about 25 protesters waved signs along Veterans Memorial Highway in Hauppauge during rush hour. “Your time is up,” read one sign with a photo of Gross.

John Carracci, who co-founded Enforce the Animal Laws in November 2014, said he quit the Suffolk SPCA that year after six months as an investigator.

“They skated around doing anything the right way,” he said. “They didn’t have the manpower for investigations, and they didn’t have the experience for investigations. There was one guy — me — full-time, handling 30 cases every two days.”

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Gross said he has 90 volunteers, including peace officers who investigate cases.

Despite what critics want, Gross said his agency isn’t folding.

“If they don’t like what we’re doing, call the police department,” he said. “I wish there was no animal abuse and nobody would call us. That’s when I would like the SPCA to shut down.”