JACK SILVERMAN figures that along with his sister and brother he "probably decimated one of the finest Indian collections there ever was."

Out of ignorance, of course. Silverman grew up on a 32-acre estate in Lake Geneva, Wis. His father, Eddie Silverman, who brought talking pictures to the movies, bought the home, complete with American Indian artifacts, from the previous owner. The children, who still own the house and what's left of the Indian collection, used to shoot the bows and arrows, throw the tomahawks at the pottery and dress up in the ghost shirts.

Silverman thinks his two-year-old ethnological museum in Aspen, Colo., is "penance" for what he destroyed.

The expensively appointed mini-museum is located on the second floor of a modern building over a gourmet shop and a kitchen boutique. The exhibit is principally made up of rare southwestern Indian weavings: Chief Blankets and serapes made by Navajos. The blankets and serapes were worn by wealthy Indians of that tribe and traded to others. One blanket was worth "20 horses, 2 black slaves and a wife," according to Silverman. Today one of the oldest ones, dating back to the early 1800s, might sell for as much as $100,000, or even as Silverman said, "the same 20 thoroughbreds they were worth in 1820."

The best of them were made before 1885, Silverman said. There were never that many, he added, because there were "only 50 weavers at most." By the end of the 19th century trade between southwestern and northern Indians died off "because of the railroad, the Civil War, Manifest Destiny and annihilation of the Navajos." By the turn of the century the weaving became coarser and the blankets became rugs.

The wealthy 39-year-old curator began collecting modern paintings in the early '60s. He says he "doesn't know what brought on" his switch from modern art to Chief Blankets. And he is reluctant to talk about the possible reason - his involvement, he says, in helping the Indians with their claims against large coal and oil companies. All he will say is that he "loved that part of the country and traveled there."

But he is very open about the mistakes he made when he started collecting blankets. "I was looking, touching, feeling everything, going to every trading post. I started selling all the art and buying all the wrong weavings, klutzy weavings made in 1900 and 1920, excellent examples of a lousy period.

"I got rid of them and kept only these," "These" are the 25 on display and some unspecified number of others, which Silverman will only describe as "dozens."

The serapes are longer than wide and have a hole in the middle for the head. The Chief Blankets are wider then long and were worn over the shoulders. Both are displayed at the museum on forms as if they were draped on a human body not laid flat or hung on a wll. According to the magazine American Indian Art, the Chief Blanket, "one of the finest achievements in Navajo weaving . . . was designed to be worn, to drape regally and to move gracefully. When displayed flat, it appears somewhat static; but wraped around the human body, if flows elegantly, and as the body moves, the design becomes as kinetic as a mobile sculpture."

In the winter Silverman gives a short tour to museum visitors most afternoons after 3:30, when he descends from the ski slopes. He doesn't have to make his living from the museum. Silverman's family fortune was made by his father who opened a chain of movie theaters in Chicago. Eddie Silverman's children run the Essaness Corp. now, which has diversified into television and real estate. Jack, a bachelor, is chairman of the board. He maintains a residence in Chicago as well as Los Angeles, but has spent most of the last eight years in Aspen because of the skiing. He goes to Chicago when business demands.

The museum, however, does support itself on the serigraphs that Silverman makes of the weavings. A major in telecommunications at the University of Southern California, he learned silk-screening "on the side," he said.

Each of the 16 different serigraph series is based on a different blanket. The editions are limited to 100. The individual prints sell for $250 each, handsomely framed in doweled oak. Silverman said he plans to add two more designs every year. To help sustain his operation, Silverman hopes to do contract work for other museums as well.

His prints are on display at the Heard Museum in Phoenix; Buffalo Bill Historical Center in Cody, Wyo.; Millicent Rogers Museum in Taos, N.M.; The Laboratory of Anthropology in Santa Fe, N.M.; the Art Institute and Field Museum of Natural History in Chicago; the Museum of Fine Arts at the University of Utah and the British Museum.

Silverman would like his museum to be "a prototype of a museum for profit that can work as a one-man operation." Besides an interest in art, all you need is a lot of cash.