Maryland State Police will begin a crackdown on speeding motorists today, concentrating on commuter traffic and using unmarked foreign cars, radar-equipped aircraft, increased and more visible patrols and "rolling roadblaocks."

The six-month experimental program estimated to cost $200,000, is part of Gov. Harry Hughes' energy conservation program, announced April 20, which the governor called "the most stringent that has been implemented by any state." The theory is that motorists will conserve fuel when forced to slow down.

Forty-two extra troopers will be assigned statewide to enforce the 55 mile-an-hour speed limit. In the Washington area, 25 to 30 troopers will monitor traffic on parts of the Capital Beltway-especially near Pennyslvania Avenue-on Routes 50 and 270, and on other highways as manpower permits.

"In the past we didn't get after the commuter," said Thomas Smith, superintendent of state police. "We don't want to stop anybody from getting to work. But we want them to comply with the spped limit and we're going to force them to do so.

"They'll just have to start five minutes earlier," he said. "Generally, Maryland commuting speeders travel just five miles over the speed limit."

Police have ordered additional radar sets, all of which can detect speeders driving in traffic lanes opposite to the direction a police car is travelling. A light airplane and a helicopter will monitor traffic from the air, and police will travel in unmarked trucks, vans and foreign sports cars. In areas of massive and chronic speeding, police will create a "rolling roadblock" by driving two or more police cars in tandem at the head of traffic at 55 miles an hour.