A 55-minute chunk of the Washington-Houston football presentation was knocked off NBC Television yesterday after a power failure at RFK Stadium.

The electrical feed between the stadium and the network's mobile units was the only power supply affected by the failure, said Ken Hopkins, the stadium manager.

Hopkins and network officials at the game were at a loss to explain the cause of the blackout, which led, according to a telephone operator at WRC-TV here, to "millions of" calls from irate viewers.

It took 40 minutes to restore power, related Allan Henderson, NBC technical director, because workmen had to move about 300 feet of television cable from the original connection to another hookup almost halfway around the outside of the stadium.

Henderson said that power was lost at 1:35 p.m. and restored at 2:15, shortly before halftime. The network did not rejoin the contest until almost kickoff for the second half.

At that point, television play-by-play announcer Jim Simpson told his public the power failure occurred because "a switch in the main power box went off at the stadium".

"If the main switch had gone off," said Hopkins, "we would have lost everything. It was one feeder out of 800 feeders in the building."

"I don't want to point my finger at NBC and say it was their equipment. And I resent them pointing fingers at us. Simpson announced it was our fault. It was a mutual problem. We reacted to it in a timely manner."

Larry Cirello, producer for NBC, relayed all inquiries to Henderson, a technical director at NBC for the past 34 years. The switchboard at network affiliate WRC-TV told callers that the Potomac Electric Power Co. (PEPCO) had lost all power to the stadium.

Hopkins said he was told that NBC was using three three-ton air conditioning units in its trucks. After the power failure, Hopkins said NBC reported to him that the network was using only two of the units.

However, Hopkins said, even with the three air-conditioning units functioning at the same time, the total load used by NBC should have been only 190 amperes of current. Hopkins said that NBC had requested -- and was given -- 200 amperes, the usual request for a game.

As a National Conference team, the Redskins normally are carried by CBS. However, in interconference matchups, the game is shown by the network that normally covers the visiting team. Thus, in this case, it was NBC.

CBS has its own cables permanently installed. However, Henderson said, the cables used by CBS and NBC are not compatible. Thus, NBC set up its cables in a different part of the stadium.

Hopkins said stadium electricians and part of the NBC crew helped move the cables. He said if there had been another connector hookup near the original hookup, the switch likely could have been accomplished in 5-10 minutes.

Henderson said that the only time NBC brings its own electrical supply is when the network knows none will be available at the site. He said that was the case last week when the network transported a diesel-powered generator to Rahway (N.J.) State Prison to provide the necessary power for a boxing match there.