An "insomniac's"' bicycle tour of Washington - starting at 1 a.m. and ending with a sunrise breakfast on the steps of the U.S. Capitol - is being planned for Sunday, Aug. 28, by a group of tireless two-wheeled environmentalists from New York City.

Similar to the popular middle-of-the night tours of Manhattan held annually for the past eight years, the midnight ramble will bring more than 100 New Yorkers here on Amtrak, their bikes stacked in a baggage car, plus additional bicyclists from Philadelphia and Baltimore.

he insomniac tour is open to any Washingtonians wishing to spin aound a dark, cool and virtually deserted Nation's Capital and willing to contribute $1 each to help plant trees in New York's Central Park.

Leading the pack on the 14-mile route along Pennsylvania Avenue to Rock Creek park and back through the Mall - with stops at deserted historic spots along the way - will be Elizabeth Moynihan, wife of Sen. Patrick J. Moynihan (D-N.Y.), Henry Hope Reed, former curator of Central Park and Micahel George, CBS television editor.

The purpose of a midnight tour of Washington is to bring New Yorkers to see the "magnificent job" the National Park Service has done with parks in the Nation's Capital and to focus attention of the Carter administration and Congress on the "disastrous" condition of Central Park and most of America's other urban parks, says Robert Makla, a Wall Street lawyer and one of the founders of Friends of the Parks in New York.

"We'd like to see Central Park . . . where there's been no tree care for 30 years and the park's in terrible condition . . . taken over by the Park Service,"Makla says. "The Park Service has made Washington a model for the nation, the foremost city park systrem in America."

The Friends of the parks, a 12-year-old volunteer group which has raised about $20,000 for tree planting and care in Central Park and four other city parks, is particularly concerned about the two dozen major U.S. urban parks designed in the 19th century by Frederick Law Olmsted, says Makla.

"Almost all of Olmsted's parks are in a shambles - Belle Isle in Detroit, parks in Boston and dozens of other cities and Central Park," which in the mid 1850s became the first major park created in this country, Makla said.

The Friends of the parks midnight ride here will end with breakfast - sandwiches squished into biycled bags - on the west front terrace of the Capitol, also designed by Olmsted. It too is threatened, and would be virtually destroyed by the proposed extension of the Capitol.

The tour, which will be held rain or shine, was set on a full-moon night to help light the bicyclists' way. The tour will start at Union Station when the train arrives shortly after 1 a.m.

This summer's annual insomniac tour of Manhattan, held July 17, attracted 500 bicyclists and raised more than $400 for Central midnight walking tour of lower Manhatten and Brooklyn Aug. 14, starting at 2 a.m. and ending with breakfast in Olmsted's Prospect Park in Brooklyn.

For further information about the Washington middle-of-the-night tour call Alexandrian J.P. Nicolais, at 354-5804.