The state’s highest court heard arguments this week in a widely-watched land use case that will ultimately decide whether a swath of rare coastal heathland along Moshup Trail in Aquinnah will remain forever wild or be opened up for development.

The complicated 18-year-old case involves arcane issues of law and is the first of its kind to be heard by the Massachusetts Supreme Judicial Court. The outcome could potentially have far-reaching effects on land titles throughout the town of Aquinnah.

Lead plaintiffs in the case are Aquinnah landowners James Decoulos and Maria Kitras, who want to establish their right of legal access to two landlocked parcels off Moshup Trail totaling about 30 acres. To reach their land from the public road, they are seeking an easement through conservation land. Without legal access to a public road, a property cannot be developed. They are joined by another plaintiff group that includes Aquinnah landowners Mark and Charles Harding.

Defendants include the town of Aquinnah, the Vineyard Conservation Society, the Martha’s Vineyard Land Bank, the state of Massachusetts and several private property owners, among them Caroline Kennedy and her husband Edwin Schlossberg Jr.

For many years the town, VCS, land bank and state environmental affairs office have been involved in a conservation project aimed at protecting the heathlands surrounding Moshup Trail. At the same time, Mr. Decoulos and Ms. Kitras have been battling the town on numerous legal fronts over their development plans around the trail.

The case argued this week, which has bounced back and forth between the land court and the state appeals court since it was first filed in 1997, is a window into the history of the town. Until the late 19th century, much of the land in what is now Aquinnah was held in common by members of the Wampanoag tribe. In the late 1800s the Massachusetts legislature took steps to provide tribal members with the same rights as other citizens in part by incorporating the town of Gay Head. In 1871 and 1878, in a process called partition, commissioners appointed by a probate judge divided the entire town into 700 setoff lots, deeding them to tribal members. The commissioners made provisions for access to peat bogs and to Menemsha Pond for fishing, but no other access provisions were included.

The landlocked lots owned by Mr. Decoulos and Ms. Kitras are old setoff lots. The question before the court is whether the lots have an implied access through a legal doctrine known as easement by necessity. The defendants argue, among other things, that many of the 700 setoff lots changed ownership after they were first given to tribal members, and that easement rights should and could have been negotiated as part of the purchase.

An earlier ruling by the land court found there is no easement by necessity since the lots were originally held in common. This year the state appeals court overturned that decision, finding that the long custom of sharing access had the effect of establishing an equivalent chain of title on the lots.

The state Supreme Judicial Court later granted further appellate review.

On Tuesday morning this week, seven justices for the SJC, led by Chief Justice Ralph D. Gants, heard arguments from five attorneys involved in the case.

The hourlong court proceeding was broadcast live on the internet by the Suffolk School of Law.

Peppered by questions from the justices, the attorneys strayed into an array of intricate legal issues and struggled to stay within the brief time allowed for arguments.

“Easement by implication . . . it’s a rare animal . . . and difficult to prove,” said Jennifer Roberts, the longtime environmental attorney for VCS.

‘This was part of an entire town — 700 lots,” said Diane Tillotson, representing the land bank. “Necessity was extinguished at the time of the original conveyance.”

“But isn’t that a matter of dispute?” asked Justice Barbara A. Lenk. “There is some question about what the practice actually was.”

Ronald H. Rappaport, representing the town of Aquinnah, recounted history. “We’ve had more than 100 years of real estate transactions [since the setoff lots were created,] and this never came up,” he said. He pointed to the Indian land claims settlement approved in 1983 and ratified by the state legislature and Congress a few years later. The settlement cleared titles on all land in Gay Head, which had been under a cloud for nine years following a lawsuit filed by the Wampanoag tribe in 1974. The lawsuit had challenged the validity of the setoff lots under another, older federal law, the 1790 Nonintercourse Act. Mr. Rappaport said when the settlement agreement was approved, any aboriginal rights on the setoff lots were extinguished. “If you don’t recognize the land court . . . . every lot in town will be subject to [an implied] easement over their land. That is completely not acceptable,” he said.

Wendy Sibbison, representing the lead plaintiffs in the case, said the setoff lots created by the probate court in the 1800s were clearly intended to convey inalienable property rights to the tribal people. “This statutory scheme was part of a historic effort to restore them to the status of humans,” she said. “The purpose of this was to allow Native American people to alienate land.”

But Justice Geraldine S. Hines returned to the question of whether the common use presumption ran with the setoff lots. “Is this the equivalent of a chain of title?” she asked.

Ms. Sibbison appeared to downplay any broader implications, focusing squarely on the two lots owned by her clients. The lots are separated from Moshup Trail by two other lots, one owned by the town, one owned by VCS, both of them conservation land. “We only need access to one of them to gain total access to our lots,” Ms. Sibbison said.