Gov. Harry R. Hughes ordered new restrictions today in the heating and air conditioning of Maryland's public buildings as he unveiled an energy conservation program he called "the most stringent that has been implemented by any state."

In an executive order signed today, Hughes also directed state police to step up their enforcement of the 55 miles-an-hour speed limit on major highways and instructed government agencies to reduce gasoline consumption by at least 10 percent.

Hughes said these actions were "taken in the spirit of being prepared" for a national energy crisis. He said several recent events-including the accident at the Three Mile Island Nuclear plant in Pennyslvania and the recent political unheaval in Iran, a major oil supplier for the United States-made it "more obvious that states must act now, before the long lines appear at the gas pumps."

Hughes said he has drafted a second executive order-restricting the heating, lighting and air-conditioning of commercial buildings-that will be signed May 15 if several neighboring states agree to implement similar measures.

Hughes said he has sent copies of this order to the governors of all 50 states and to Mayor Marion Barry of the Distrit of Columbia. The governor said he would not sign the second, more restrictive, order unless the District of Columbia and Virginia agree to impose similar measures. "That," Hughes said, "will insure that no exceptional or unique disadvantages is being imposed on Maryland citizens."

The energy program that Hughes put into effect today has five main features:

All nonresidential government buildings, state and local, will be required to set a maximum temperature of 65 degrees during the cold months and a minimum temperature of 80 degrees during the warm summer months. At night and during weekends, the maximum heat will drop to 60 and the minimum air-conditioning will go up to 85 degrees.

Similar Measures were imposed for public buildings in Maryland during the natural gas shortage of 1977 and the coal strike in 1978. In both instances, however, the orders were enforced for only a few weeks. Hughes said the new order will be enforced "indefinitely."

The state police will intensity their enforcement of the 55 miles-an-hour speed limit.To accomplish this, Hughes said, six additional officers from each of the seven state police barracks will be assigned to the speed limit enforcement program.

State agencies and departments must reduce their consumption of gasoline by at least 10 percent. To help accomplish this, Hughes directed the Department of General Services to increase the number of subcompact cars from the current 14 percent to at least 25 percent of the state fleet.

The state highway administration and local public works departments are directed to turn off all street and parking lot lights they feel are not "absolutely necessary" for public safety.

Fuel suppliers must give regular reports to the state on their inventories. This directive was originally imposed during the oil shortage in 1973, but has not been enforced in recent years.

The second executive order, if imposed next month, would extend the heating and air-conditioning reductions on all private nonresidential buildings. It also would restrict outdoor display lighting to one sign identifying the commercial establishment-and that sign could be lighted only when the establishment is open for business after dark.

"These measures are not heroic or drastic," Hughes said at a State House press conference this afternoon. "They are to date, however, the most stringent proposed or implemented by any state." If the entire program is properly enforced, Hughes said, the state will reduce its energy consumption by at least 5 percent a year.

Hughes called his program "a homespun job" that was put together without assistance from the Carter administration, which recently presented to Congress its own federal energy conservation package. He said that in many areas the state program would be stronger than the federal proposal-particulary if the heating and airconditioning reductions are applied to commercial buildings. CAPTION: Picture, GOV. HARRY R. HUGHES " . . . states must act now"