Harvard is fighting what may be a losing battle against a serious increase of often-fatal Dutch elm disease, in an attempt to preserve the Yard's leafy canopy.

The object of the battle is to prevent the disease from spreading by removal of the heavily-diseased elms and treatment of less diseased and certain specimen trees. But since the success of the treatment is erratic and the affliction is so widespread in New England, the removed trees will be replaced not by other elms, but by varieties of oaks and locusts.

Eighteen Removed

About 18 elms have been removed from the Yard in the past two years, Diane K. McGuire, landscape architect for Buildings and Grounds, said yesterday. The treatment of less diseased and some specimens started last year. The results of the treatment are not yet known.

There is no known cure for Dutch elm disease.

The problem of the affliction has been serious for the past few years, McGuire said. "DDT was one of the best controls, and ever since its use was banned the disease has been rampant," she said. The disease is carried by the elm bark beetle, which DDT kills.

Another possible reason for the increase in the incidence of the disease in the Yard in the past few years, McGuire said, may be the increase in pollution. "Mass Ave runs along two sides of the Yard. Pollution lowers the vitality of trees and makes them more susceptible to disease," she said.

The Department of Buildings and Grounds will replace the removed elms according to a tree plan which McGuire's office has been working on over the past year. There will not be a new tree planted for every one removed. "Some of the trees were too close together," McGuire said.

One of the objects of the plan is "to keep a canopy similar to the one we have in the Yard now," McGuire said. There are 288 trees in the Yard, of which 101 are elms, the most common species. McGuire said she does not know how many of them are diseased, because the affliction cannot always be detected in its early stages.

Buildings and Grounds will start planting the new oaks and locusts in the fall. "If the research on Dutch elm disease goes well," McGuire said, "we may be able to use elms again."