The leap second of 1988 -- added by the U.S. Naval Observatory at 6:59:60 p.m. New Year's Eve to synchronize the Earth's rotation with its clocks -- may already have changed the lives of some prominent Washingtonians.

Think of it: A whole extra second this year in which to take a second thought, look before you leap, run instead of fight, change your mind, take the first step, stop the whirl and get off and, of course, make split-second decisions.

Washingtonians may have used the second in various ways, or in the new fashion for thrift, saved the second to spend later, according to their needs.

For example, Gary Hart had an extra second to get visitors out the back door or off the boat before being caught by the camera. Or he could have saved it to use to decide to leave the presidential race.

Senators who may have tabled their leap second to use later to parley two seconds longer on the floor will now be a second later to dinner parties, occasioning leap seconds extra of sighs by hostesses all over town.

As a result, roast beasts will be one second better done, a glorious effect for such as Clement Conger and current company, who are the only two in town who like their meat dead and done.

Design Cuisine's Bill Homan and his partner, executive chef Horst Klein, who in 1987 received the Royal Order of the Perpetual Pear, perhaps in a split second might decide to pare down menus.

Having already brought Washington such new customs as sitting down at cocktail parties and wearing napkins at dinner, Warren Robbins, founder of the Smithsonian's Museum of African Art, had an extra second to pursue other social innovations -- such giving teas instead of cocktail parties.

Rosalynn Carter, a woman who can make up her mind in a half-second, perhaps will decide to run for president to continue her crusade for the mental health of the nation, not to mention the White House Preservation Fund, both of which have suffered greatly in her absence from Washington.

Nancy Reagan could use hers to invite First Decorator Ted Graber to redecorate the East Room in California Comfortable style before she lets her successor move in.

J. Carter Brown, director of the National Gallery of Art, may yet take his leap second to accept a starring role in a new television epic, "Secrets of the Receiving Line."

Robert McCormick Adams, Smithsonian secretary, could possibly use his to abolish receiving lines altogether in favor of actually talking to guests.

Armand Hammer, the Occidental Petroleum oracle who helped bring us Mikhail Gorbachev, may bank his second to use to receive the Nobel Peace Prize for his lifetime work as a go-between. Everyone on his 1988 Christmas list will receive a Technicolor film of the event.

The Gorbachevs themselves, who took their time about arriving at the White House, might have to spend their leap second waiting for return visits from the Reagans at the Moscow summit this year.

This year's denouncement of black tie by Philip Merrill and Gorbachev's refusal to wear the formal attire may, in the leap second available to hostesses all over town, result in one more come-as-you-like party.

Ellen Merrill, having signed up everyone in Washington for her "Hello My Name Is Ellen Merrill" Association (of people who always give their names when meeting even their dearest lovers and most hated enemies), will add a subgroup of masters who will, in the Japanese fashion, hand over their cards to everyone upon meeting, including their spouses and children.

Letitia Baldrige and Judith (Miss Manners) Martin will each plan to write new etiquette books solely devoted to the subjects of black tie/white tie. Liz Carpenter will then take her extra moment to do an outline for a book on how to be happy though tieless.

Sen. Paul Simon will use his extra flash to come out squarely for bow ties for all occasions, causing ties in many polls.

Gretchen Poston, who as Rosalynn Carter's social secretary caused a snow machine to whiten the White House lawn, may, as a partner in Washington Inc., the whirl-around-the-world corporate events planners, arrange for all of Washington to be covered three feet deep in spun sugar for the Amalgamated Association of Sweet Daddies convention.

All fruitcake lovers will leap to the defense of their favorite Christmas cuisine, brandishing serrated cake knives at those who dare to despoil the name of the fair recipe in public while gobbling it up in private.

And multitudes of Washingtonians will spend their leap second thinking up ways to squander money on Leap Year Day, Feb. 29, 1988