East Coast pet owners have joined their veterinarians this year in an all-out war against fleas, which have invaded houses in numbers seldom seen before.

Homeowners and veterinarians all around the Washington area have reported that the flea problem intensified this summer.

"It's been terrible this year," said Dr. C. Bruce Morley of the Rocky Gorge Animal Hospital in Laurel. "Last year was bad, but this year has been ultrabad."

Pet owners have even expressed their frustration in letters to the editors of local newspapers and offered suggestions for getting rid of the bloodsucking parasites.

The explosive flea situation has left dogs scratching, cats itching and their owners wondering where the fleas came from.

"We've even had people come in whose children have been badly bitten by fleas this year," Morley said.

He said two types of fleas are causing the problems this year: the samller cat flea and the larger dog flea.

Morley said the flea problem has "a lot to do with changes in the spraying programs that are done by the counties and state."

"Since the ban of DDT, the insecticides used are not as effective as the ones in the past," he said. "I guess that's because of environmental regulations."

The rainy weather last summer also gave fleas an ideal breeding ground because they live longer in wet areas, according to Dr. Harry Schultz, a Baltimore veterinrian.

Flea season basically runs from the end of May to the beginning of October. But the fleas can live year round in a house.

Once inside the house, the fleas hav a "captive audience" in the dog, he added.

Flea collars -- which are advertised as flea killers -- are also part of the problem, Morley said.

"People put a collar on their dog and think that's going to be the end of the problem," he said. "They just don't work too good."

Morley said he has sold three times as muchinsecticide spray this year and about five times as many foggers -- a $5.95 aerosol bomb that kills live fleas in the home.

"We haven't been able to keep them in stock," he said. "I'm sold out of everything to use against fleas."

Schultz says he has seen a 50 percent increase in the flea problem this year.

Fleas feed on an animal's blood and then get into carpets to lay their eggs, which hatch 21 days later, Morley said.

"If you get rid of the dog because of the flea infestation, you have a house full of flea eggs," Schultz said. "They'll hatch and they'll have no dog to go to so they feed on you."

Both veterinarians suggest that pet owners use a good flea controlling substance on the dog as well as their homes.

"If you use it just on the dog, the fleas from the carpets will get on them," Morley said.