When Mildred B. Bliss died in 1969, leaving Harvard sole custodian of what had been her elegant Washington, D.C., home and 16-acre garden, she stressed in her will that the estate's trees were "not to be neglected or lightly destroyed."

That stricture has come back to haunt Harvard in the past few months as persistent opposition has forced the University to reconsider its plan to build an underground library beneath the formal garden.

In 1940 Bliss and her husband, Robert W. Bliss, formally transferred their estate, Dumbarton Oaks, to Harvard to house the Center for Byzantine Studies. Later a collection of pre-Columbian art and a library of garden design were added.

Known for Garden

But Dumbarton Oaks is best known for its formal garden, which both critics and proponents of the current plan agree is one of the most beautiful in the world.

In February Harvard unveiled a plan to expand the Byzantine library by building beneath the North Vista terrace next to the main house. The architect, Hugh Newell Jacobsen, maintained that the plan would cause no permanent or substantial damage to the garden.

Critics of the project are led by Peter Schenk, a former Dumbarton Oaks gardener who resigned his position in order to protest the plan. He claims that the underground library would destroy much of the beauty of the terrace, which he said is unique and perfectly proportioned.

Elizabeth Rowe, a former head of the National Capital Planning Commission, the Committee of 100 on the Federal City, Washington's oldest planning group, and the Potomac chapter of the American Society of Landscape Architects, have joined Schenk's cause.

Their pressure last month forced President Bok to delay construction and delegate Charles U. Daly, vice president for government and community affairs, to conduct a review of the situation.

Four Options

Daly said yesterday he expects to reach a decision sometime in May. He has four options: he could recommend to proceed with the original plan, to build on another site, to scrap all plans or to build on the same site but sink the building five feet deeper, which some say would result in less damage.

All involved in the controversy agree that the original plan would require the destruction of at least four weeping cherry trees and two Himalayan cedars.

Schenk calls the cedars "irreplaceable" but Harold Goyette, director of the Planning Office, said yesterday that the trees "do not relate symmetrically" and that one of them is "poorly shaped."

Schenk and Rowe both contend that the damage could extend far beyond the site itself. Forging an access road through the garden, they say, and rolling in heavy construction machinery is bound to destroy shrubs and feeder roots even if few trees are chopped down. Moreover, they say, construction workers may not operate with perfect delicacy.

"You can tie a blue ribbon to a tree," Schenk said, "but if some asshole on a crane backs into it, some asshole on a crane has backed into it, and Jacobsen can't bring it back."