A large tract of rare and secluded oceanfront land owned by the Kennedy family in Aquinnah has been placed on the market for sale.

Two undeveloped lots totaling 93 acres from the 377-acre Red Gate Farm were listed for sale this week. One lot is about 53.5 acres, fronting the Atlantic Ocean, with an asking price of $25 million. The second lot is 39.5 acres with more than 1,000 feet of frontage on Squibnocket Pond, deeded beach access off Moshup Trail and an asking price of $20 million.

Red Gate Farm is owned by Caroline B. Kennedy and Edwin Schlossberg. Ms. Kennedy’s mother, the late Jacqueline Kennedy Onassis, purchased the property in 1978 from the Hornblower family for $1.1 million.

Located between Moshup Trail and Squibnocket Pond in the westernmost reaches of the Vineyard, the Kennedy family property has long been used as a quiet summer retreat. The property is home to at least a dozen protected species found throughout its windswept, salt-blasted dunes, freshwater ponds, coastal heathlands and extensive pond and ocean frontage. The property has remained largely undeveloped since Mrs. Onassis bought it 35 years ago. It is believed to be one of the most ecologically rare areas in the state.

In 2006, Ms. Kennedy and Mr. Schlossberg created a subdivision plan for the property, reducing the number of lots from 34 lots to seven for family estate purposes. The Martha’s Vineyard Commission reviewed and approved the plan as a development of regional impact (DRI).

The subdivision created a 100-acre lot surrounding the current family homestead, as well as three lots ranging from 30 to 50 acres for each of the three Kennedy-Schlossberg children. One 60-acre beach lot was designated as permanently unbuildable, and two lots of 39.5 and 53.5 acres were created for future sale.

The commission said the two lots could not be subdivided if they were sold outside the family, and development of more than three houses on any of the lots would require further DRI review.

In the plan, the Kennedy-Schlossbergs also agreed to preserve more than 300 acres by restricting potential development to less than 15 per cent of the property, and to donate money to the Massachusetts Estuaries Study. The family also voluntarily made a $100,000 donation to the Aquinnah housing committee.

Any development on the lots now for sale would also be subject to strict review. The land lies in four districts of critical planning concern, special overlay planning districts with added regulations for environmental protection. Development would be subject to review by town boards and the Massachusetts Natural Heritage and Endangered Species program.

During the subdivision plans, Ms. Kennedy told the commission that her family was committed to taking care of the unspoiled land. The purpose of the estate plan was not to develop the land, but to guarantee it would be passed on to her children, she said.

In approving the decision in 2006, the commission said “the owner’s stewardship of the land is part of the reason the land is such valuable habitat.”

The Massachusetts Endangered Species Program describes Red Gate Farm as one of the most important pieces of land in the commonwealth. It is home to two federally-listed endangered species and at least a dozen protected species, including the arethusa orchid and the northern harrier.

The listing agent for the property is Deborah Hancock, owner of Hancock Real Estate in Chilmark.

At a public hearing in 2006 when the commission was reviewing the subdivision plan, former Vineyard Conservation Society executive director Robert Woodruff spoke in eloquent and almost emotional terms about the Kennedy property. He described rare orchids and northern harriers, thousands of tons of sand that are moved by the wind every day, and beech and holly trees that are possibly more than 100 years old.

“I spoke to [Natural Heritage ecologist] Tim Simmons a week or so ago, and we talked about this property,” Mr. Woodruff told the commission at the time. “We both shook our heads in amazement at what we’ve been privileged to see.”