Talk to people in education and public health and they will say the number of children with autism is surging.

But other than anecdotal evidence and scattered numbers from agency to agency, there is no real way to tell if there is an increase in the cases of autism.

"We don't have any data source that's available to us that would allow us to say there's an increasing trend," said Robert Knorr, deputy director of epidemiology at the Massachusetts Department of Public Health.

The DPH is preparing to do the first official count of cases of autism beginning sometime next year, said Knorr, in part because so many parents were calling and asking about the increase in cases.

Debate rages around the cause of the disorder, which appears to be afflicting more children at alarming rates. A recent California study reported a 272 percent increase in a 10-year period.

The DPH began meeting in November to discuss methods for the count, which will largely rely on a Department of Education database. Knorr said the DPH will have to determine whether the database is an accurate way to do the count.

The Department of Education probably has the best handle on numbers of children with autism because each school district is responsible for determining the appropriate education plan needed for children with disabilities.

Audrey Seyffert, assistant superintendent for pupil services in the Natick schools, said there are 35 autistic children in the district. Seyffert said the definition of autism did not exist until the early 1990s. Before that, children were diagnosed with some other form of developmental disability.

"There are more kids being diagnosed," she said. "Twenty to 30 years ago we weren't diagnosing them with that."

Seyffert said a count could be helpful, depending on how the definition of autism is used and how the count is conducted. Part of the reason there is a national debate about incidence of autism is because people are measuring differently.

Vincent Strully Jr., executive director of the New England Center for Children, a program in Southborough serving 224 autistic children and adults, said he does not believe the prevalence of autism has increased, but that the public's awareness of the disorder has.

Autism, or autism spectrum disorder, is characterized by a range of behaviors that make communicating or socializing difficult. The behaviors include yelling, outbursts and bolting from a room or conversation. It is usually evident before age 3.

Other characteristics include "self-stimulating" behaviors like humming, flapping of hands or fingers and distracted eye movements. Some people with autism have "restrictive interests" like repetitive activities or a fascination with numbers.

The spectrum includes other forms of the disorder like Asperger's and pervasive developmental disorder or PDD.

Experts in the field say a count would help direct funding for treatment and educational plans.

"There's just a real lack of services," said Strully. "There are hundreds of people we turn away every year."

Larry Tummino, associate commissioner of the Department of Mental Retardation for field operations, said there are 2,296 people under the age of 18 in the state with autism. Of these, 203 are in 10 MetroWest towns and receive services from DMR.

Tummino said his agency will work with the DPH to get an accurate count of the numbers of people with autism, but said it will be difficult to gauge an increase or decrease because the way autism is diagnosed has changed.

"That partly may be the case for the rise in numbers," he said. "It does seem like there's a higher incidence rate than there used to be."

Dr. Margaret Bauman, director of an autism clinic in Wellesley, said that of the 250 children she sees a month, two-thirds to three-fourths are diagnosed with some form of autism.

If anything, Bauman said she believes autism is being under-diagnosed.

"It's really not clear whether there's an increase or not," she said. "Most people in mainstream science feel there is not."

Dania Jekel, executive director of the Asperger's Association of New England (AANE), said she is hoping a count will gauge the extent of autism and help direct services.

"We have no idea how many people (there are)," she said. "We know the numbers are huge. We just can't tell if there's an increase of it (or) if it's staying the same. For us it's crucial information."

Asperger's Syndrome has characteristics similar to autism, but those with the syndrome have normal IQs and a greater ability to communicate verbally.

Jekel, whose association is based in Newton, said there are more than 4,000 people on the mailing list, which also includes professionals. The AANE adds about a hundred people a month to the list and gets about 15 to 20 calls a day.

Strully said about 30 to 35 percent of 224 students at his center are from out of state.

Experts agree there seems to be an increase, but are unsure if it is because physicians have improved their diagnosis of autism or because the definition of autism has been broadened to include other disorders not previously counted.

Strully said it might be difficult to get an accurate count since a count has not been done in the state before and, therefore, no baseline exists to show if numbers are increasing or decreasing.

"What they need now is an accurate count of the prevalence," Strully said.