Without many of us realizing it, the Tennessee Valley Authority, that almost 50-year-old federal experiment in providing cheap electric power, has begun acting like the privately owned giants of industry.

The agency took a look into the future, decided nuclear power is here to stay, and went out and got involved in uranium mining so that it could guarantee itself a supply.

This aspect of the TVA's operations was made clear by a notice in the Sept. 10 Federal Register (page 45233) that describes how the agency intends to prepare an environmental impact statement for a uranium mine it hopes to start near Marquez, N.M.

The TVA's partner in this enterprise turns out to be the Kerr-McGee Nuclear Corp. Under a 1974 agreement, Kerr-McGee would operate the mine and the two partners would share equally any uranium produced. The site's reserves are estimated at 6.8 million pounds and if the mine proves out, the partners expect to begin production, at about 800 pounds a day, "no earlier than June, 1984," according to the notice.

A question to TVA headquarters reveals that this is far from the authority's first venture in uranium mining.

The TVA's interests date back to 1972, an official said, and today, the authority owns "extensive" properties in Wyoming, South Dakota and New Mexico.

In fact, the TVA is about to close down another uranium mine it has been working since 1978 because the world market price has dropped so low that it is uneconomic to keep the mine open. But should the price go back up, that mine and another one--owned in partnership with Mobil Oil Corp. and also in New Mexico--could go into production.

The reason the TVA has gone into uranium in such a big way is that its uranium needs for four nuclear units, and one expected to come on line next year, are so great. According to a spokesman, it takes about 1 million pounds to start a reactor, and another 400 to 500 pounds every 12 to 18 months after that.

The mine that is about to be closed provided about 2 million pounds in two years, just about enough to meet current TVA needs, but not nearly enough to protect the authority for the future.

The Marquez mine is expected to meet TVA needs through 1990, and, according to the spokesman, the TVA is studying its other properties to see where its uranium will come from after that.