Halloween, once a time for childish abandon, is this year a time for wariness, due to widespread fear of food tampering. In the Washington area, law enforcement officials urged extreme caution, and at least 40 cities around the nation have canceled the holiday altogether.

The fear is that persons might put foreign objects or poisons in foods and candies they give to trick-or-treating youngsters, and apprehension has been heightened by recent incidents in the Chicago area in which someone contaminated capsules of Extra Strength Tylenol with cyanide, killing seven persons.

Several hospitals in Maryland and Virginia announced free X-ray services for parents wanting to check their children's treats for metal objects.

In Prince George's and Montgomery counties, where Halloween officially was observed last night -- the District and Northern Virginia counties have designated today as the official celebration -- police officials reported trick-or-treating activity was lighter than in recent years. However, some officials said they expect goblins to visit tonight in many neighborhoods.

There were no unusual incidents reported last night by area police or hospitals.

"Everything is quiet," said D.C. police Sgt. Anthony Mitchell, minutes before he received a telephone call from his Silver Spring home, assuring him that his children had returned home safely with bags filled with Halloween treats.

Although concerned about the danger of tampered candies, Mitchell said he was not overly troubled. As in past years, he said, his 11-year-old son and two daughters, aged 9 and 5, were only permitted to trick-or-treat under an adult neighbor's supervision.

"But I told them to stay in our block, and they are not to eat anything until I get home and check it out," he added.

"The kids aren't even worried about it," Mitchell said. "I think adults are more worried."

A poll by Potomac Survey Research Inc., a Bethesda-based polling firm, asked 559 Marylanders -- who were being questioned on their preferences in Tuesday's election--about the effect of the Tylenol scare on Halloween.

Among those responding, 10 percent said they planned no action regarding candy or treats that their children collected, allowing them to eat whatever they liked; 20 percent said they would not allow them to eat the treats under any circumstances, and 16 percent said they would allow them to eat the treats only after parental inspection.

Wanda Taylor, 24, a secretary for the Department of Defense interviewed on Deane Avenue NE in Washington yesterday, said she would not allow her 4-year-old son Mark to go out Halloween.

Like other parents interviewed, she expressed anger and tension about food tampering. "I just think it's dangerous to allow kids to go trick-or-treating unless you know your neighborhood very, very well," she said.

And Wilma Deen, mother of a 2-year-old daughter, who was attending a block party yesterday in the 1300 block of N Street NW said: "Some of the excitement of it is gone. You can't go out at night and move around freely."

But as dusk turned to evening yesterday, many of the area's older "children" converged on Georgetown for their annual night of play.

"Anybody out here tonight doesn't have both oars in the water," D.C. police reservist Gene Markus remarked as three multicolored "ballerinas" with glittering hair beat two genuine Army privates to a cab.

"We're just wandering around and having a blast," said Larenzo Pike, 18, of Fort Dix, N.J. "I love it," he said as his eyes followed a score of people, including some resembling Union soldiers, a pair of aliens from an unspecified planet, a few Chicago-style gangsters and a Miss Piggy.

By 10 p.m. police had given up on controlling the bumper-to-bumper traffic with stop lights, and half a dozen D.C. police officers were directing the waves of people and vehicles at Wisconsin and M streets NW.

The U.S. Food and Drug Administration said there have been 270 reports through Thursday of possible tampering with products since the Chicago Tylenol incident.

In Baltimore, a supermarket security guard was arrested yesterday after a razor blade was found imbedded in a tomato. Police said Scott Andrew Behlert, 18, of Baltimore, was charged with adulterating food products, a felony that carries up to 20 years in prison.

Baltimore police said they were testing the contents of a 16-ounce bottle of Coke turned in by a woman who said she detected an ammonia-like smell when she opened it.

In other parts of the country, banks reportedly were having a run on coins by people seeking to substitute them for edibles that might be suspect and that probably would go to waste because parents would not allow their children to eat them.

Towns and cities throughout Ohio, Pennsylvania, Massachusetts and Illinois banned trick-or-treat activities altogether. In Louisiana, Ascension Parish and Hammond city officials also announced a ban on all trick-or-treating by children, with extra patrol cars being sent out on the streets to enforce the ban.

In New Orleans, some groups were organizing parties to substitute for on-the-street activities. Others were asking residents to hand out low-cost trinkets, balloons and decorations left over from the Mardi Gras festival, in place of foods.

Other communities have a long history of discouraging trick-or-treating and are redoubling their efforts this year. In Houston, unsupervised street activity has been discouraged ever since a young boy died eight years ago after eating cyanide-laced candy, a crime for which his father was later convicted.

In Detroit, according to wire service reports, a woman found a razor blade in a hot dog, the latest of several such incidents involving pins or blades. As a result, according to the reports, Hygrade Ballpark Hot Dogs suspended production at its Detroit plant and recalled packages out on store shelves supplied from the Detroit plant to stores in Michigan, Illinois, Indiana, Ohio and Pennsylvania.

Carnival Products was reported to have recalled 1 million candy apples after 9-year-old Terry Thorstienson of Park River, N.D., said he found a pin in one such apple.

In New England, brownies from the Peggy Lawton bakery of Walpole, Mass., were recalled, reports said, after a woman in Franklin, N.H., ate part of a brownie apparently tainted with Demerol, a chemical painkiller.