One of the most awesome of all wildlife migrations is beginning in a quiet, inauspicious way, and nature lovers don't have to go to some lonely Hawk Mountain to get a glimpse.

It could be as close as their own backyard.

A week and a half ago on the Chesapeake Bay, 10 miles below the Bay Bridge, a clutch of people on boats were determinedly pursuing sea trout. Through this melange a brightly colored scrap floated on the wind.

This insect, no bigger than a sliver of crepe, was a monarch butterfly making its way south, probably to Mexico.

Then another appeared. And another. The captain of the boat pointed one out. "In a few eeeks we'll be seeing hundreds of them," he said.

Indeed, these orange and black flyweight beasts will be congregating by the millions in the high mountains of central Mexico in a few months' time. Thousands will pass over Washington and Kent Island and Arlington, McLean, College Park and Hyattsville, flying solo in their custom.

A hundred of them weigh barely an ounce, and yet some will flutter on for up to 2,000 miles, following an instinct to carry on the breed.

Dr. Lincoln Brower of Amherst College in Massachusetts has spent 15 years studying monarchs. Even he remains awed by their journey.

"It's incredible," said Brower, who last week was organizing a scientific expedition to follow the monarchs to Mexico this fall. "There are many butterfly species that migrate, but nothing anywhere compares to the monarch."

The distance is remarkable, but the phenomenon that most impresses Brower is the fact that the monarchs now moving south are as much as four generations removed from the ones that flew north in the spring to give them life.

They have no leaders to show them the way. And yet they will fly to some of the very same fir trees in the high Mexican forests that their grandparents and great-grandparents occupied the winter past.

For monarchs, it's nice to be born in the fall. That way they get to live perhaps eight times as long as their parents.

Summertime offspring have a lifespan of up to a month, but the ones born now -- in September and October -- are left with the job of propagation. Most of them will over-winter in a semi-dormant state south of the border, and fly back in spring to deposit their eggs on sprouting milkweed plants, six, seven or eight months later.

Among local butterfly aficionados is Robert T. Mitchell of University Park, retired from the U.S. Fish and Wildlife Services Patuxent Research Center and author of "The Golden Guide to Butterflies and Moths."

He has dedicated his farm on Maryland's Eastern Shore to the research and preservation of butterflies.

He said the migration in the Washington area has indeed begun. "I got a report from some hawk-watchers last week who saw as many as 100 monarchs moving south," he said. It should reach a peak around the first week of October.

Mitchell's favorite way to find monarch flight paths is to drive west to east across the Eastern shore. When a monarch flits across the road he stops and waits for more. Sometimes they come steadily all day, sometimes they don't.

Both he and Brower have been involved in projects of tagging monarchs. Tiny paper tags are pasted on the butterfly's wings in hopes that it will be collected somewhere and data on flight patterns can be obtained.

Of course, returns are rare.

"In bird-handling projects we figure a return of one percent is good," said Mitchell.Butterfly returns are only a tiny percentage of that.

But tagging helped in the discovery of the primary wintering habitat for East Coast monarchs, which was made only a few years ago. The find was the result of an expedition coordinated by Dr. Fred Urquhart of the University of Toronto, his region of Canada being the northern edge of monarchs' summering habitat.

Urquhart's crew found an incredible sight in the mountains of central Mexico, where millions of sleeping migrant monarchs lay glued to tall firs. Urquhart reported his discovery in the August, 1976, National Geographic, and Brower considers the discovery "the most important scientific breakthrough in the study of monarchs in the 20th century."