Over the past three decades, hundreds of thousands of Americans who used to consider themselves white or black have taken on a new identity: Now they are American Indians.

This phenomenon of changing selfhood has baffled and intrigued demographers investigating the forces that have more than tripled the American Indian population since 1960. But in the Indian community, there is little mystery in the heightened desire to proclaim a piece of native lineage.

"For many decades, it wasn't fashionable to be Indian," said Bob Ferguson, historian for the Mississippi band of the Choctaw Indians. "If you had Indian ancestry, you didn't admit it. Now, it's all-American."

The steep trajectory of growth among American Indians -- from 523,600 in 1960 to an estimated 1.8 million today -- is showing up in the 1990 census. While the natural growth of the Indian population in the 1980s should have ranged from 25 percent to 33 percent nationally, virtually all the state figures released so far show much higher rates.

In New Jersey, hardly known as a concentration point for Indians, the group's population increased more than 78 percent to just under 15,000. In Virginia, the growth was 62 percent; in Texas, 64 percent; and in Missouri, 61 percent.

"There was a big increase between 1960 and '70, and a whopping increase between 1970 and '80," said Matthew Snipp, a demographer of American Indians at the University of Wisconsin. "It sounds like we've got another big jump between '80 and '90."

While some of the increase can be attributed to high birthrates and improved counting by the Census Bureau, experts surmise that a substantial portion is the result of shifting self-identification, most of it among urban Indians with little connection to a tribal organization.

Demographers believe, for example, that more than 300,000 people who had not identified themselves as American Indians a decade before did so for the first time in the 1980 census, accounting for about half the growth over the 1970s.

"There is a very large pool of people out there who have some degree -- in many cases rather small -- but some degree of American Indian ancestry," said Jeffrey Passel, a demographer at the Urban Institute. "What we have is an increasing fraction of those . . . choosing to answer the race question as American Indian."

Brenda Dardar Pitre, reared in an Indian settlement outside Golden Meadow, La., and now working in an Indian education program at the local school, said she believes some of those who have recently identified themselves as American Indians may have just discovered their ancestry, while others have been inspired by a renewed sense of ethnic pride.

But some, she argued, are "hoping to get some benefits" in federal programs or payments that may come to tribes like hers, the United Houma Nation.

None of it is surprising, she said, given the history of discrimination suffered by her people.

"When I started school, they said to my mother, 'She's white, isn't she?' " said Pitre, 32. "That was their way of trying to fit us into a white society."

And when families identified their children as white, she said, "they weren't trying to say their children should be ashamed, they were trying to protect their children. No parent wants their child to be an outcast."

The American Indian population has traced a remarkable descent and rise since the days of Columbus. Conservative estimates put the population at 3 million to 5 million in 1492, although some estimates are many times larger, according to Snipp. The population, decimated by disease imported by white settlers and war, bottomed out at about 228,000 in 1890, and has been rising since.

Passel, who previously worked at the Census Bureau, in recent years has tallied birth certificates and subtracted death certificates issued for American Indians state by state. As a result, he and other experts were able to calculate what the population growth should have been since 1960. (Immigration, which accounts for much of the growth among Hispanic and Asian Americans, plays virtually no role in the increase of American Indians.)

What the demographers found was stunning: The 1980 census should have shown 1,055,000 American Indians, based on the so-called natural increase of births minus deaths. Instead, the number came in 34 percent higher, indicating that as many as 357,700 persons changed their race to American Indian over the decade.

The same had been true to a lesser extent in the 1970 census, when the figure was 67,000 higher than it should have been by the natural increase, a gap of 9.2 percent.

Passel found that the biggest changes were showing up in states without large Indian populations.

"This shift in identity wasn't occurring on the reservations of Arizona, but it was occurring in the cities in the East, where there were not large concentrations of tribally based Indians," Passel said.

The geographical distribution confirmed that the large increases could not be attributed to improved counting, although it is known that the Census Bureau has undercounted Indians in the past.

"If it was just that the counting had gotten better, you'd have expected the increases to be in a place where there are lots of Indians . . .

Arizona and South Dakota, instead of occurring in Vermont and Mississippi," Passel said.

The extent of this shifting self-identity is in some ways a logical extension of the large numbers of Americans who claim they have some Indian blood. When a sample of Americans was asked in the 1980 census about their ancestry -- a question separate from that asking one's race -- 7 million people claimed some Indian ancestry. A 1979 survey found 10 million claiming they had some American Indian heritage.

Much like the resurgence in cultural pride among blacks and Hispanics in the 1960s and 1970s, the American Indian Movement and other forces spurred a new interest in Indian heritage that continues today.

"There's a renaissance," said Gay Kingman, executive director of the National Congress of American Indians. "There's a return to our language and our music and our dances. We're teaching Indian in our schools. Tribes are more self-governing, so more people are identifying themselves as Indian."

Wayne Ducheneaux, president of the Indian congress and a member of the Sioux tribe in South Dakota, calls some of these latecomers "closet Indians" and others, he said, may not be Indian at all.

Don Sharon, chairman of the Florida tribe of the Eastern Creek Indians, cites another factor -- the desire to share in the services, fishing rights and other benefits awarded to American Indians in recent decades. When his tribe and others won payments in the 1960s in a legal settlement with the federal government over land rights, many people came forward and tried to prove their Indian heritage, he said.

"When there was money involved, then people started identifying themselves this way," Sharon said. "Everybody had the streak of greed in them."

State...........1980...........1990......Percentage Change

Alabama........7,583.........16,506.................117.7%

Arkansas.......9,428.........12,773..................35.5%

Hawaii.........2,768..........5,099..................84.2%

Indiana........7,836.........12,720..................62.3%

Louisiana.....12,065.........18,541..................53.7%

Mississippi....6,180..........8,525..................37.9%

Missouri......12,321.........19,835..................61.0%

Nebraska.......9,195.........12,410..................35.0%

Nevada........13,308.........19,637..................47.6%

New Jersey.....8,394.........14,970..................78.3%

Rhode Island...2,898..........4,071..................40.5%

South Dakota..44,968.........50,575..................12.5%

Texas.........40,075.........65,877..................64.4%

Vermont..........984..........1,696..................72.4%

Virginia.......9,454.........15,282..................61.6%

Wyoming........7,094..........9,479..................33.6%

NOTE: American Indian population includes Eskimos and Aleuts. The states included on this graphic are those for which racial breakdowns from the 1990 Census have been issued

SOURCE: Bureau of the Census