On Feb. 28, if a Maryland restaurant chose to serve margarine and call it butter, describe its frozen haddock as fresh or claim its vegetable soup was made from scratch when it came from a can, it made little difference to the state. But all of that changed March 1 when Maryland's truth-in-menu regulation went into effect.

The regulation is similar to ones in effect in many city, county and state jurisdictions, most notably Los Angeles County where "what you see, better be what you get."

On the first day the new law went into effect in Maryland there did seem to be a certin amount of confusion among both restaurant inspectors and restaurateurs. The former weren't quite sure how to proceed, especially in what has been described as "the difficult gray areas," the latter were often not even aware of the new law.

Actually the law is not new, Authority to require truth in menus or other types of food advertising such as newspaper ads and billboards, was established by the Maryland Food, Drug and Cosmetic Act of 1970 but not implemented until last week. The part of the law which has to do with sanitation was put into effect first; now the mislabeling part is being phased in. The gray areas are forcing the health officials to move slowly.

For instance, even though Arby's sells a "roast beef" sandwich and the roast beef is pressed beef, not a single slab of roasted meat, the law is hazy on whether or not that is deceptive advertising. The same holds true for turkey roll sold as turkey or chicken roll sold a chicken, according to the chief of Division of Compliance and Enforcement of the State Department of Health and Mental Hygiene.

Ronald Nelson said: "There is no state standard of indentity for meat and until the state sets standards" these items "fall into a gray area."

Whether Maryland fried chicken must come from Maryland or the name refers to a style of cooking is another questionable distinction. "But," Nelson said, "if a Maine lobster came from New Jersey it wouldn't be a problem because the species would be different."

An inspection trip through Montgomery County on the first day of the new law found one restaurant without any violations; another where the owner was told he could not call his soup "homemade" even if it was made in the restaurant kitchen. But Nelson said the inspector was wrong. If a product is made in the restaurant it can be called homemade because people think of "products cooked in that establishment that way."

In a seafood restaurant visited by the Montgomery County inspector a number of menu changes were called for. The inspector, however, told the restauranteur he would take the menu with him and discuss the problem areas with his supervisor.

The menu advertised "fresh fillet of haddock" but all the haddock in the back was frozen; there was no fresh red snapper either though it was described that way on the menu. The "fried fresh deep sea scallops" were also frozen.

Nelson said the first six months of the program are "a grace period." Under Maryland law when a restaurant is cited for a violation it also has a certain period of time in which to comply before any action is taken. After that the restaurant's license can be suspended. In addition, for the first offense the owner can be fined $10,000 and receive a jail term of up to a year.

For "blatant" violators the fine could be as high as $25,000 with a three-year jail term.

But the Maryland Restaurant Association, which represents about 1,000 of the 12,000 restaurants covered by the new regulation, says it can live with a truth-in-menu regulation.