A federal jury yesterday ordered the Blake Construction Co. Inc. to pay more than $12.6 million in damages to a subcontractor that had teamed up with Blake in 1972 on construction of a new Walter Reed Army Medical Center.

During a six-week trial in U.S. District Court, U.S. Industries Inc., the subcontractor, contended that Blake failed to properly supervise and manage the job, which resulted in long delays and heavy losses for the subcontractor.

The jury of two men and four women deliberated for about 2 1/2 days. The aware is believed to be one of the highest in a civil damage suit heard in federal court here.

U.S. Industries, which is headquartered in New York, engages in various construction contracts under the trade name Federal Sheet Metal. That firm held a subcontract to install air conditioning, plumbing and heating at the Walter Reed site.

Blake entered a partnership agreement with U.S. Industries in order to meet bonding requirements needed to qualify to submit a bid on the Walter Reed project. Without the backing of U.S. Industries assets, Blake could not have been able to get the job, according to court records.

A consultant hired by U.S. Industries to review work on the project in 1974, concluded that Blake was not properly supervising subcontractors' work on the new medical facility. Some construction delays, for example, occurred because faulty concrete pillars had to be replaced at the direction of an independent testing laboratory.

U.S. Industries had contended that Blake's delay and disruption of Federal Sheet Metal's work resulted in additional expenses for labor, office overhead, equipment and material costs and increased financing costs.

Blake had contended during the trial before Judge Gerhard Gesell that the delays were principally caused by actions of the Army Corps of Engineers, which had solicited bids for the construction project and awarded the project to Blake. Blake had bid $108 million on the Walter Reed project.

Blake and the Corps had arranged a schedule by which Blake would be paid each month for the work completed. U.S. Industries maintained in its lawsuit that Blake withheld monies paid by the Corps which were due to Federal Sheet Metal for work it had done.

Collister Johnson, an attorney for Blake, said yesterday that he believed the verdict was "contrary to the evidence in the case" and added that his clients would challenge the jury verdict.

The Blake Construction Company, one of Washington's largest construction firms, is owned by Morton, Stanley and Howard Bender.