Stonehenge, that monumental enigms where tourists have always been able to rub shoulders with history, is destined to become yet another cordoned-off sightseeing attraction.

Plans are being implemented by England's Department of the Environment to limit access to the circle area where the big stones stand and rest silently holding their nearly 4,000-year-old riddle. The reason for the restriction is not the rubbing of tourist shoulders - after all, the 50-ton slabs can take that. But the sometimes destructive curiosity of nearly three-quarters of a million visitors a year has caused concern for the preservation of the monument.

Or as S. J. Walton, secretariat of ancient monuments for the Department of Environment, put it:

"Visitors sit and walk on the recumbent stones and climb on the standing ones; they rub and finger the incisions representing weapons on the stones, and even carve their initials on them."

Walton said that the density of the crowds makes adequate protection of the stones by custodians impossible "unless we increase the policing to an unacceptable extent."

Gravel in the circle area, now temporarily closed, has also had an abrasive effect on the stones. The gravel replaced turf some years ago because the grass was often a sea of mud due to England's frequent showers and the many tourists. (The area covered by gravel is now being returfed. A protective path way through the circle is already under construction to restrict direct access to the stones. This work ios expected to be completed by early May, a Department of Environment spokesman said last week.)

Walton said that there would probably be a rope barrier outside the circle area and special arrangements for a limited number of visitors after normal visiting hours. Better interpretive facilities (models and display boards) will be provided and parking, concession and other facilities will be moved to a new site farther away from the monument.

Walton said the new parking and facility area would no longer infringe on the monument itself. To this U.S. visitor, the facility area never did seem to infringe. The concession stand, for example, is hidden from public view. An American tourist also notices that the entire area is devoid of neon. There are no fast-food outlets, cocktail lounges, motels and the like, which are usually part of the landscape around U.S. tourist attractions.

With its hundreds of thousands of visitors annually, Stonehenge has been a good income source for the Department of Environment. Entrance charges were put on a seasonal basis in 1976, and the income nearly doubled to 154,955 pounds, which included some extraordinary expenses that year. The excess admissions money is used for other momuments that don't draw nearly as well but still require maintenance and policing.

The off-season pricing was introduced to try to lure more visitors during the non-tourist season, from October through March. The current April-September fee is 40 pence (77 cents) for adults. In the off-season it's 10 pence. The price is well worth it. One need possess only a drop of curiosity to wonder about the stones' purpose. (Some authorities believe there was an astronomical alignment associated with regilious ceremonies.)

Stonehenge is about nine miles north of Salisbury. It's an easy day's journey from London. by train, the trip starts at the Waterloo station. a bus that leaves from the Salisbury train station goes directly to the site. However, the best way to get there is on foot.

So I took a bus from the center of Salisbury and for 42 pence rode to Amesbury. From there, it was about a two-mile walk to Stonehenge, probably the most delightful two miles I have ever stepped of. The paved walk runs through quaint Amesbury, past an old church complete with graveyard, over a literally babbling brook, past thatched-roofed houses and yards with the usually magnificent English gardens, by fields where cows stand motionless and pheasant hide. In the background is that neat, fully utilized, green-on-green hilly English countryside.

About a half mile from the destination, the asphalt walk reaches the crest of a hill. There one looks down on Stonehenge for the first time. The view is splendid. The ruins stand alone. The mystery is unfolded.

MIller is a free-lance writer. He lives in Chevy Chase.