Julia Martinez is a full-blooded Santa Clara, a member of a small Indian tribe in northern New Mexico whose distinctive culture has been traced back at least 700 years.

Now a dispute between Martinez, an obscure potter, and the tribe has evolved into what the Justice Department terms "a troublesome and significant issue that warrants the . . . attention" of the Supreme Court.

The issue, in essence, is whether the right of individuals to the equal protection of the laws should yield to the right of Indian tribes with sovereign powers of self-government to decide who their members shall be.

Specifically, can the Santa Clara exercise its tribal sovereignty to exclude from membership the children of an mixed marriage in which the Santa Claran is a woman while admitting to membership the children of a mixed marriage in which the Santa Claran is a man?

Since 1680, the tribe has existed as a conquered people, encapsulated first in Spanish and then in American surroundings.

Inevitably, the alien milieu and such developments as the automobile eroded some customs and traditions of the Santa Clara community, or pueblo.

Yet the tribe managed to preserve its basic culture, including the practice of its own ancient religion and the use of its traditional and official language, Tewa.

Mixed marriages had been rare. They began to increase after 1930, when Santa Clara children started to attend Indian schools with members of other tribes.

In 1935, after mixed marriages had started to put a strain on the tribe's economic resources, the tribe amended its constitution to provide for case-by-case decisions on whether the children of such marriages would become members of the tribe.

This was a sensitive and important matter: Only children who are members can inherit reservation land and property; only children who are members will be allowed to participate in the pueblo's political life.

Under the case-by-case approach, some children of marriages between Santa Clara women and outsiders became members. But in 1939, after a sharp increase in mixed marriages, the tribal leaders took a step that would predestine the dispute with Martinez.

They passed an ordinance under which all children of a male Santa Claran's marriage with an outsider - white, black, yellow, or simply from another tribe - automatically become full members of the Santa Clara pueblo; all children of a female tibe member who marries an outsider are barred from membership. This formalized patrialineal - through the father - descent, which is a feature of most Indian tribes and other cultures.

Two years later, Martinez married a full-blooded Navajo, a machinist who drives from the 48,000-acre reservation along the banks of the Rio Grande to his job in Santa Fe.

They had 10 children. Two died including a daughter, Natalie. Because she was not a member of the tribe, the federal Bureau of Indian Affairs, operating under a policy it abandoned in the late 1960s, denied medical care to Natalie when she was terminally ill.

Starting in 1946, Julia Martinez began trying to persuade the tribal leaders to enroll her children, all of whom are accepted into the ancient religion, speak Tewa, and practice traditional customs.

She was a lifelong resident of the pueblo; she wanted the children to be. The pueblo is their full-time home, but if she were to die before them, as in all likelihood she will, they would pace the possibility of expulsion. And, of course, she wanted the children to be able to inherit her property.

In 1963, after 17 years of failure, she stepped up her campaign into a vigorous and almost unrelenting effort.

Trying to get her daughter Audrey enrolled, for example, she asked her representative on the tribal council to bring up the matter at a tribal meeting. He refused; she got special permission from the governor of the tribes to address the council. She and other women promoted a special meeting of the entire pueblo. She met with BIA officials. She sought help from the Senate Subcommittee on Constitutional Rights.

But nothing worked. So in 1972, after retaining a lawyer, she went off the reservation, in a near-literal sense: she went into U.S. District Court to sue her own tribe. The court should rule, she contended, that by denying membership to the children of women who intermarry, the tribe denies the children the equal protection of the lawa incorporated in the Indian Civil Rights Act of 1968.

After concluding that the court had jurisdiction over this extraordinary case, Judge Edwin L. Mechem ruled for the tribe.

"In deciding who is and is not a member, the Pueblo decides what it is that makes its members unique, what distinguishes a Santa Clara Indian from everyone else in the United States," Mechem held.

"Much has been written about tribal sovereignty," Mechem said. "If those words have any meaning at all, they must mean thata a tribe can make and enforce its decisions without regard to whether an external authority considers those decisions wise.

"To abrogate tribal decisions, particularly in the delicate area of membership, for whatever 'good' reasons, is to destroy cultural identity under the guise of saving it," he said.

What of the equal-protection promise in the 1968 law? It must be read against the background of tribal sovereignty, law and custom, Mechem said. Other courts consistently have held that it is not identical to the constitutional guarantee of equal protection in the 14th Amendment, he said.

The Tenth U.S. Circuit Court of Appeals reversed. In sponsoring the 1968 law, Sen. Sam J. Ervin Jr. (D.-N.C.) in tended to incorporate the constitutional guarantee to the extent necessary to assure that Indians have the same rights in relation to tribal authorities that other Americans have in relation to state authorities, the court held.

Julia Martinez's children and others in the same class are victims of "plan discrimination," the appellate court held. To approve it "would be tantamount to saying that the Indian Bill of Rights is merely an abstract statement of principle."

The intermarriage problem could have been solved without invidious discrimination, the court said. All the tribe had to do was to treat equally the children of all mixed marriages.

The tribe - in a case styled Santa Clara Pueblo vs. Julia Martinez - petitioned the Supreme Court to review the case. Several Indian organizations supported the petition. One, the Ail-Indian Pueblo Council, said the appeals court decision "has the potential of upsetting or destroying entire social structures . . ."

Last Jan. 25, the Supreme Court invited the views of the United States. In a brief last month, Solicitor General Wade H. McCree said the disagreement over how to interpret the Indian Civil Rights Act "is sufficiently important to merit final resolution by this court . . . Tribes and their members need to know with greater certainty the kinds of relief that federal courts can grant . . ."

In a footnote, the brief pointed out that it is only recently "that non-Indian culture has . . . begun to accord women equal treatment under the law."

The court is expected to decide soon whether to review the lower court decision.