Less than a mile from the U.S. Capitol in Northeast Washington there lives a wonderland with 70,000 dazzling azaleas with pink, purple and crimson blossoms, trees that grow for hundreds of years, cherry trees bursting with pink blossoms, valleys filled with thousands of ferns, and giant fluorescent orange and yellow fish that live to be 200 years old swimming peacefully in aquatic gardens.

Hidden amid the gas stations and warehouses of New York Avenue and a huge apartment complex on Bladensburg Road, the 444-acre National Arboretum thrives in sequestered splendor.

"We are the least known of the major museums in Washington," said Marc Cathey, director of the arboretum, which has 87 gardens and collections on its rolling wooded hills.

The arboretum wears two faces. To scientists it is a laboratory for creating, growing and studying new plants. To visitors it is a floral retreat perfect for walks, picnics and family outings.

Spring bathes the arboretum in deep purples, pinks, yellows and reds as dogwoods, peonies, wildflowers, lilacs and rhododendrons blossom.

Recently visitors enjoyed hillsides brimming with brilliant colors as the azaleas reached their peak.

Meanwhile, roses, irises and herbs are quietly preparing to blossom next week.

As early as 1901 a commission, which later became the U.S. Commission of Fine Arts, was established to plan a botanical garden-arboretum in Washington.

It wasn't until 1927, however, that an act of Congress mandated what is now the National Arboretum "for purposes of research and education concerning tree and plant life."

"We have the largest collection of landscape trees and shrubs in America," Cathey said. "We also have one of the few programs that actually sends plant collectors throughout the world to find new species of plants."

There are more than 1,000 volunteers around the world who help collect plant samples and seeds for the arboretum, which specializes in plants that grow in temperate climates.

"That's why we do so much research in the Orient -- the climate is very similar to ours" in the United States, Cathey said. About 80 percent of the arboretum's landscape plants originated in the Orient.

"On the grounds of the arboretum we have accessions [samples] of almost 60,000 different types of plants," Cathey continued.

"One of the very important purposes of the arboretum is that we are a repository of plants for the future," he explained. In fact, approximately 30 new types of trees will be introduced by the arboretum this year.

The arboretum's beauty is best viewed by meandering through its 10 miles of paved roads. Each year about one million visitors find their way to the arboretum, which is bounded by the Anacostia River, Bladensburg Road, New York Avenue and M Street NE.

"I think the arboretum is great," said Robert Hickman, who traveled from Dover, Del., last week with his wife and friends for a visit. "It's the only opportunity to see so many types of plants that you can't see anywhere else," said Hickman, who was the Delaware state plant pathologist for 37 years before he retired.

That same day, Betty Lunsford of Columbia, Md., toured an exotic Japanese flower exhibit. "For them to have the foresight to save this land in the middle of Washington was just wonderful. I come here all the time," she said.

The arboretum is also a joy to researchers. Theodore Dudley, one of three research botanists at the arboretum, said it may be "the only research facility in the world that specializes in the history, development, biology, taxonomy and nomenclature of cultivated plants."

The arboretum's herbarium, a scientific research facility, has more than 500,000 dried pressed plant specimens from throughout the world. Some of those specimens date to 1750.

"We even have some specimens that were collected by [American explorers] Lewis and Clark" in 1804, said Eric Neumann, director of education at the arboretum.

The scientists also breed and develop new trees, shrubs and other plants that can withstand air pollution and sudden temperature changes.

The 53 bonsai trees donated by the Nippon Bonsai Association of Japan are among the most impressive collections. Most of the tiny, delicate trees are more than 100 years old, and the great-granddaddy of them all is a Japanese white pine that is over 360 years old.

"The bonsai collection is just amazing," said Evelyn Edson, who teaches a class in Japanese culture in Charlottesville and visited the last week with her class. "I've never seen anything quite like that 360-year-old tree."

A staff of 80 researchers, groundskeepers, botanists and administrators maintains the arboretum, which includes two facilities in Maryland -- one on 80 acres in Glenn Dale and other on 200 acres in Beltsville. The arboretum, which operates on an annual budget of $3.8 million, is the only federally funded arboretum in the country.

"We're using so much of our land to build shopping centers and parking lots that in a few years our grandchildren won't even know what a plant looks like, especially plants like these," said Ruth Virdin, of Clayton, Del., during a recent visit to the arboretum. "That's why a place like this is so important."