New no-smoking regulations went into effect yesterday in Prince George's County for thousands of grocery and retail stores, restaurants, movie theaters and doctors' offices.

But county officials said the law will not be enforced or its $25 fines levied for about 30 days because many establishments are still unaware of it and few have posted the required sings. Officials now are preparing thousands of information packages on the law to mail to the businesses.

Giant Food Stores were among the few places yesterday to be in compliance with the law, according to John Koontz, acting director of the county health department's environmental engineering section.

The law, which was passed in August, progibits smoking in theaters, doctors' offices, hospitals and clinics and retail stores with eight or more employes. This includes most grocery stores, drug stores and other commercial establishments. Large restaurants -- those seating more than 75 persons -- must set aside no-smoking areas, a clause that affects about one-third of the county's 1,600 licensed restaurants, including a number of carryout restaurants like McDonald's, Koontz said.

The law, prompted last summer by a request from the Bowie chapter of GASP (Group Against Smokers Pollution), is similar to regulations in Howard and Montgomery counties.

Montgomery's regulation, which does not cover restaurants but has a $50 fine, became law in May 1977. "We've only had two prosecutions under it that I know about and there has been substantial compliance with the law," assistant county attorney A. Katherine Hart said yesterday.

Both Prince George's and Montgomery allow small restaurants and retail stores not covered by the law to decide whether to be covered. Koontz said many stores want the regulation because of the danger and damage caused by smoking customers.

Both laws also exclude private offices, thus permitting smoking in a room. Smoking also is prohibited in public areas of county-owned or leased buildings or private buildings where public meetings are held.

But there are exceptions. Smoking is permitted at dinner theaters and restaurants which "are an integral part of bars," under the presumption that drinking and smoking traditionally go hand-in-hand.

And one retail establishment where smoking is permitted, regardless of the number of employes, is the tobacco shop.