IT'S NOT a weapon that a thief normally would use in a robbery - at least not without a lid on it to keep it from spilling.

Cops said yesterday that they were looking for two men who have attacked clerks in at least 16 convenience stores in Pennsylvania, New Jersey and Delaware by throwing hot liquid into their faces.

Three of the thefts took place in Philadelphia.

The thieves' weapon of choice has been scalding coffee or hot chocolate, which they purchase in the stores, cops say. Some of the victims suffered serious burns.

"In my 37 years of reading police reports, and studying criminals and crime, I have never heard of something like this," said Lawrence W. Sherman, director of the Jerry Lee Center of Criminology at the University of Pennsylvania.

Despite the imaginative twist the robbers have put on their crimes, the heists have not been lucrative. Striking in the early hours of the morning, there's not usually much cash in the registers.

The first Philadelphia incident happened Feb. 10 shortly before 5 a.m. at the 7-Eleven on Harbison Avenue near Tulip Street in the Northeast, police said.

"We always take extra safety precautions here," said a clerk at the store who asked that her name not be used.

"I mean, it was 4:45 in the morning. Nobody has that kind of money in their drawer that they would be after. That's why he didn't get much," she said.

The second, police said, happened Feb. 13 shortly after 1 a.m. at the 7-Eleven on Mascher Street near Louden, also in the Northeast.

"It makes me a little nervous," said a clerk there. "Although most of them happened in the early morning, there is no telling when something like this could happen again."

Just two hours later, the robbers struck again, this time at a Wawa on Columbus Boulevard near Tasker Street in South Philadelphia.

Police Sgt. D.F. Pace, of public affairs, said that in each the attacks there were several employees in the store, but the crooks waited until there were only a few customers.

"It doesn't really seem to matter to them who is in the store; they are just looking for the best opportunity," Pace said.

However, he said, "They always seem to wait until there is only one clerk at the cash register."

A clerk who was splashed with hot liquid had to be treated for third-degree burns of the face, another for second-degree burns after his face started to blister and swell, police said.

With the easy availability of guns and knives in the area, why would someone choose scalding-hot liquid as a weapon?

Sherman has an explanation. "Robbery is generally not an economic crime; it definitely has to do with power," he said.

"It can be reflective of anger, the desire to inflict pain, and the power of the offenders to assert themselves in a sort of psychopathic way."

Sherman said a motive could be defiance of the mega-corporations that run the convenience stores.

But, he said, the thieves must know that the people who are hurt by these tactics aren't chief executive officers sitting in plush offices, but clerks who generally work for low wages.

Police described the robbers as men between 18 and 25, both of medium height and weight.

Wawa and 7-Eleven have offered $10,000 for information leading to the arrest and conviction of those responsible.

Anyone with information about the heists should dial 911. *