Reddy Kilowatt is a public figure in some ways and not solely a private symbol for use by large utility companies, a U.S. judge ruled here yesterday.

The ruling allows a public interest, nonprofit group based in Washington to continue to use caricatures of Reddy Kilowatt in their materials criticizing large utility companies and power projects.

Reddy, a stick figure of simulated lightning bolts with a light bulb for a nose and electric outlets for ears, is probably the best known symbol of utility companies across the U.S. It is the property of a Connecticut firm that was begun by Reddy's creator, Ashton B. Collins, in 1926.

The firm filed suit against the Utility Project of the Environmental Action Foundation, contending that its use of the figure was an infringement on a protected trademark that is sold for advertising purposes to 140 utility companies.

The Utility Project conceded that it used unflattering drawings of the figure, but said its use was legal under trademark laws because no one could confuse its literature with materials sponsored by utility firms. U. S. District Senior Judge Howard F. Corcoran agreed.

He said that in the context of the Project's materials, which are highly critical of power companies, Reddy Kilowatt can easily be distinguished from utility-approved materials "in connotation and overall impression."