The George Hyman Construction Co. and its nonunion spinoff, Omni Construction, have pledged $1 million to the University of Maryland to establish an endowed professorship in construction engineering management, university President John S. Toll announced yesterday.

The gift, which university officials hope to augment with $500,000 from other construction firms, is part of a major effort to get more private funds for the state university, which recieves most of its budget from the state legislature.

Robert G. Smith, vice president for university relations, said the new gift is the largest ever given to Maryland for an endowed professorship. But in the past four years, Smith said, the university has received three other gifts of more than $1 million, including an estate and a herd of Angus cattle.

Smith said the private money provides "a margin of excellence and gives us an added amount of flexibility." He said the new professorship will be part of the university's civil engineering department, which will also get some funds from the gift for graduate fellowships and research.

The Hyman and Omni firms both are owned by Clark Enterprises Inc. of Bethesda, headed by James A. Clark, a Maryland graduate and member of the University Board of Regents. Smith said Clark decided to make the gift after serving as chairman of a committee that helped redesign the civil engineering curriculum.