Washington-area police and apprehensive parents concerned about possible contamination of Halloween goodies given their children were breathing easier today after the traditional night of trick-or-treating passed here with no reports of injury or sickness induced by food tampering.

And as of early this morning, only one possible case of Halloween-item contamination had come to light locally -- that of a candied apple in which a Washington woman said she found a piece of glass or hard plastic after buying it at a Northwest supermarket. Police said the store immediately removed its supply of candied apples from the shelf and had begun an investigation of the incident.

Some area parents had been so fearful that their children might find malicious tricks in their treats last night that they kept them off the streets altogether, and police in the District and Northern Virginia, where Halloween was officially celebrated yesterday, reported far fewer costumed children roaming neighborhoods than usual.

"It's dramatic," said a North Arlington resident, who said he had three or four groups of little visitors before 8 p.m., compared with 15 or 20 groups in past years.

The fear of contaminated candy and other goodies has been heightened this Halloween following the deaths of seven persons in the Chicago area who ingested Extra Strength Tylenol capsules laced with cyanide and the subsequent spate of reports of tampering involving other food and drug products around the country.

What that means, said children and adults in the Kings Park subdivision in Fairfax County, is that Halloween isn't the holiday it used to be.

"You don't have as many people walking around," said Benjamin Gotkin, 11, who was accompanied by his mother and brother. "Everyone's being more careful. It doesn't seem to be as much fun."

Gotkin's mother, Chris, said it was her fear of poisoned candy that led her to insist that her children visit only the homes of friends and close neighbors. "Any time you see something like the Tylenol thing, you know it's going to give people ideas," she said.

Even children seemed affected by the fear.

"Last year I went all over the place to people I didn't know," said Theresa Frank, 13, who was dressed as a waitress. "This year I'm only going to places that have other kids because people who have kids aren't going to do anything."

Several hospitals in Virginia and in Maryland, where Halloween was officially celebrated Saturday night, set up special X-ray units for parents wanting to check their children's treats for metal objects. But they turned up no evidence of such objects.

At Alexandria Hospital, for example, which opened its X-ray unit to the public at 3 p.m., children and parents marched into the hospital, bags of candy in hand, and placed the bags on examination tables. Hospital employes then examined the goodies, paying particular attention to poorly wrapped candy or candy with marks or spots.

More than 150 children dressed as Pac-Man, E.T., pirates and ghosts or the like had their candy inspected by hospital radiologists dressed as Raggedy Anns and sailors. The hospital filled a large trash can with suspect candy, but hospital spokesman David Norcross said they found no harmful substances or instances of malicious tampering.

The children not only got to keep the candy, but also were allowed to take the X-ray prints home with them. "It's fun for them to see what a peanut butter cup looks like in an X-ray," said Norcross.

Some area children who were trick-or-treating yesterday evening said they were aware of their parents' fears about the candy they were collecting but were not particularly concerned themselves. Mark Coudert, 10, of Arlington, who was dressed as a gorilla, said that his parents told him not to eat any candy until he returned home. "I think maybe we're going to the hospital to check it for poison," he said.

Fairfax County police reported early in the evening that they had received several calls about possible candy tampering. They visited the homes of the concerned and picked up candy, they said, but found no evidence of contamination. A county police spokesman was unable to describe the candy.

In Baltimore, police said they were investigating three separate food contamination cases involving a pin in a pear, a sliver of plastic in a candy bar and a bottle of a soft drink turned in by a man who said it had a strange taste. No one was injured in those incidents, according to police.

And in Delaware, state police removed all candy yesterday from a home in Dover where a trick-or-treater received a pink lollipop that was discolored by an unknown white substance. The candy was to be tested at a Food and Drug Administration lab. On Saturday, a 21-year-old Clayton, Del., woman was treated and released from a hospital after biting into an unidentified orange tablet that was imbedded in a fudge bar. Police turned the fudge bar over to the FDA for analysis.

Elsewhere in the nation, pins, needles and at least one nail were reported found over the weekend in candy or food in Danbury, Conn., Milwaukee, and Norman, Okla. And in Somerdale, N.J., police said yesterday that Halloween confections contaminated with barbiturates and the dangerous animal tranquilizer PCP were served Friday at a school kindergarten party. Fifteen people, including seven children, sought hospital treatment in connection with the incident, which was reported under investigation. One of the children was admitted for observation.

An informal count by the Associated Press said that in all, more than 175 reports of sabotaged fruits and candies were compiled from more than 100 cities in 24 states. Many places canceled or discouraged trick-or-treating. New York City's poison control center was flooded with reports of suspected contamination, and about 700 children showed up at a hospital in Des Moines, Iowa, to have their Halloween collections X-rayed.

In Fort Dodge, Iowa, police said a 69-year-old carpet service owner was killed in a confrontation with a masked man who told him: "Trick or treat. Give me your money or I'll shoot."

On the other hand, a Miami mother said she and her husband decided to take their 2-year-old son trick-or-treating because she didn't want her activities ruled by fear. "I'm not going to stop living my life because something might happen," said Karen Aronowitz.