Arthur Lazarus, a lawyer and champion of legal rights for Native Americans, who won a landmark award for the Sioux Nation in its ongoing struggle involving the Black Hills of South Dakota, died on July 27 in Washington. He was 92.

The cause was complications of kidney and heart disease, said his son Edward.

Over six decades, Mr. Lazarus helped Native American tribes across the country develop their democratic institutions, reclaim lands and exercise their sovereign powers.

His work was made possible by the Indian Reorganization Act of 1934, known as the “Indian New Deal.” The act reversed decades of assimilationist policies of the United States government and allowed tribes to re-establish their tribal governments and cultures. Mr. Lazarus guided them in these efforts.

“Like any fledgling government, they needed help,” Edward Lazarus, who is also a lawyer and has written about Indian issues, said in an interview. “That meant developing a taxation system on the reservations, setting up a civil justice system, capturing water and mineral rights, and sometimes suing or negotiating with the United States government.”

This work, Edward Lazarus said, was the central legacy of his father’s legal career. It included helping to draft the Alaska Native Claims Settlement Act of 1971, which awarded to Native tribes almost $1 billion and 40 million acres on which they had lived for generations. The claim had been unresolved for more than 100 years.

While devoting himself to this work, Arthur Lazarus also devoted decades to a single legal case involving the Sioux Nation. Even though he won a crucial legal victory for the Sioux tribes, the issue remains unresolved to this day.

A treaty in 1868 had set aside millions of acres of land, most of it in South Dakota, including the Black Hills, for the Sioux. After gold was discovered on that land, Congress reneged on the treaty and seized the Black Hills in 1877.

The tribes sued the United States in 1923, seeking compensation for the land seized. After several setbacks, Sioux leaders in the 1950s sought out Mr. Lazarus and others to carry on the case.

In 1979, after more than 20 years of litigation, the United States Court of Claims awarded the Sioux $17.5 million and, for the first time in such a case, the government would have to pay 5 percent interest, for a total of $106 million.

The government objected to paying interest, and appealed to the United States Supreme Court. In 1980, the high court upheld the original Court of Claims decision and sided 8 to 1 with Mr. Lazarus.