On an early near-spring afternoon, the most famous pond in America mirrors the dark, snow-tipped pines along its perimeter. Lavender clouds soften the sky. A lone fisherman trails a line off his canoe, but the trout are not biting.

Despite the outward serenity, all is not quiet at Walden Pond, the world-renowned retreat of 19th-century philosopher Henry David Thoreau. In the 140 years since he built his one-room cabin, there to live in solitude and contemplate nature, the 62-acre pond and surrounding woods have become one of the most popular tourist spots in New England, attracting 600,000 visitors a year.

On summer days, up to 8,000 swimmers and sunbathers crowd its tiny beach. Blaring radios and beer parties shatter the peace. The vegetation is trampled and the steep shoreline eroded.

"This is a desecration of an American shrine," said Mary Sherwood, 78, a retired naturalist who is head of Walden Forever Wild. The group is pushing a bill in the Massachusetts Legislature to declare Walden a state sanctuary, banning swimming and restoring the pond "to its natural and forested condition as known to Ralph Waldo Emerson and Henry David Thoreau."

A state Senate committee voted today to study the bill further after state officials and local residents opposed it in a hearing. It is given little chance of passage this year, but proponents say they will fight on.

"Walden Pond has become like Coney Island, grossly overcrowded and misused," said Kelly McClintock, executive director of Environmental Lobby, a nonprofit group. But McClintock and most other environmental activists say it is politically impractical to ban swimming at one of the few inland bathing areas unless the state provides alternatives.

The park, which includes 350 acres of woods around the deep, clear pond, is 20 miles northeast of Boston in this affluent suburb, remembered as an intellectual mecca in the mid-1800s when Emerson, Thoreau, Nathaniel Hawthorne and the Alcott family lived here.

Thoreau moved to the pond a few years after graduating from Harvard. He lived there two years, cultivating his famous bean field and writing the thoughtful, unconventional and idealistic journals that later evolved into his masterpiece, "Walden, or Life in the Woods," "Civil Disobedience" and other works.

James Gutensohn, commissioner of the state Department of Environmental Management, which oversees Walden Pond, told the Senate committee today that when Emerson's descendants conveyed Walden to the state in 1922, the deed specified that it was for public "bathing, boating, fishing and picnicking."

"Hundreds of years ago the Indians swam there," he said. "Emerson and Thoreau swam there. It's only fair that people continue to take advantage of this wonderful natural resource."

Besides, he added, "I used to take my own kids out there."

Under public pressure, the state has undertaken a $1.2 million restoration program at the park, which has been declared a National Historic Monument by the U.S. Department of Interior.

A badly eroded section of beach has been closed and revegetated, parking has been moved across a road and two ugly concrete bathhouses have been razed. The remaining bathhouse is being covered with cedar shingles.

Most importantly, the 1.7-mile perimeter of the lake, where thousands of feet have trampled the earth into a barren pathway, is to be shored up with rocks and landscaping.

Few are more distressed by the erosion than Raymond Faucher, a forester who supervises day-to-day management of the park. "What would Henry have thought?" he said sadly, pointing to the exposed tree roots where three feet of soil has washed into the pond, leaving deep gullies along the shore.

"People come here from Japan, Poland, Ireland," he said. The cabin Thoreau built is no longer standing, but visitors have piled stones alongside its foundation for years as a memorial cairn.

Sherwood told the committee that "city mobs" have so polluted the pond that "on a warm summer day you can see human feces floating." State officials contended that the pond is unusually clean.

Local residents are divided. Francis Magurn, a retired engineer said that "a lot of people believe there's a halo over this place . . . but I'd hate to see it turned into a sanctuary."

However, Thomas W. Blanding, in a letter released by the committee, deplored the "uncaring crowds" and advocated a swimming ban, adding, " . . . Henry Thoreau, the great American prophet of preservation, is a prophet without honor in his own country."