WASHINGTON (AP) _ The number of people killed by lightning fell sharply last year, but that's no reason to relax, according to experts who warn that lightning remains one of weather's most dangerous phenomena.

''A below-average death toll should not diminish the danger of lightning in anyone's mind,'' said Richard E. Hallgren, director of the National Weather Service. ''It is the second highest weather killer in this country, and it strikes anywhere.''

For weather-related deaths, on average, only floods claim more lives than lightning in the United States.

But last year was a mild one for lightning deaths, with only 68 reported, well below the average of 97 per year.

Thunderstorms continue to be a major summer threat, however, generating lightning and hail over much of the nation, and weather experts worry that last year's low toll will make people overconfident.

Most school children, for example, learn about Benjamin Franklin's experiments with lightning. But few realize that tragedy could easily have resulted.

Indeed, in 1753, Swedish scientist G.W. Richmann tried to duplicate a lightning-rod experiment about which Franklin had written four years earlier.

The result was a direct hit, killing Richmann.

Franklin, fortunately, avoided that outcome. But people emjoying the outdoors in summertime may not be so lucky if they fail to watch for storms and take precautions.

''Lightning survival requires monitoring the weather and using common sense,'' Hallgren said. ''If you are caught outdoors in lightning, seek shelter in a large building or an all-metal automobile. By all means don't be a lightning rod by standing under a single tree or remaining in an open field or in a boat.''

The most common lightning victim last year was male and relatively young. Men and boys accounted for 53 of the fatalities and the average age of people killed by lightning was 30.

Thirty of those killed were struck while in open fields or under trees, and another 24 victims were on the beach, ballfield, golf course or fishing from a boat or shore.

Lightning occurs when the electrical charges in clouds and the ground become so different from one another that electricity begins to flow in order to restore balance.

The same phenomenon occurs with the common static discharge, when a spark jumps from the hand of someone who has just walked across a wool carpet, for example.

But when nature generates the discharge between cloud and ground, it can reach 100 million volts, burning a channel through the air as it seeks the easiest path.

Because air is a poor conductor of electricity, the lightning follows objects that reach up from the ground: trees, power poles or people, for instance.

That is why a lightning rod can protect buildings by seemingly attracting lightning strokes that might otherwise strike and do damage.

In the United States, Florida is home of the most thunderstorms in summer, and the most lightning deaths, the Weather Service noted.

That held true in 1986, with the 10 lightning deaths in Florida leading the nation.

Alabama, Maryland and Michigan each had five lightning deaths, the Weather Service reported, while there were four each in Georgia, North Carolina and Tennessee.

Oklahoma and Mississippi each had three lightning deaths, and two were recorded in Kentucky, Louisiana, Massachusetts, Ohio, Pennsylvania, Texas and Utah.

Reporting a single lightning death last year were Arizona, Colorado, Delaware, Illinois, Indiana, Iowa, Oregon, South Carolina, South Dakota, Virginia and Puerto Rico.