If you live in Maryland and have an angler in the family, treat him or her with an extra measure of kindness tomorrow because the state is dealing a double blow to fishermen on the first day of 1985.

Not only does the state's new saltwater fishing license law take effect, meaning fishermen will have to pay $5 for the privilege of dropping a line in the Chesapeake Bay, but an emergency ban on fishing for rockfish, or striped bass, also begins. Blame the legislature for the former, and the Department of Natural Resources for the latter.

Also officially on the books tomorrow are new restrictions on provisional license holders in Maryland. The law limits the nighttime hours when many teen-agers may drive alone and makes it harder to earn full driving privileges.

Though most of the nearly 1,000 laws enacted by the 1984 legislature have been enforced since July 1, some do not become state law until tomorrow.

Usually, the later effective date is chosen when a law is so complex that implementation in July is not feasible. Sometimes, though, the reason is less salutary.

Consider the teen-age driving law. After tomorrow, 16- and 17-year-olds with new provisional licenses must be accompanied by a fully licensed driver between midnight and 6 a.m. instead of 1 a.m. to 6 a.m. In addition, provisional license holders must have an unblemished driving record for a full year, rather than six months, to get a full license before the age of 18.

The new law, sought by a group of Baltimore County parents, would have taken effect last July had it not been for the objections of the vice chairman of the House Judiciary Committee.

The delegate, Arthur S. Alperstein, liked the bill except the fact that his son would have been affected. With a Jan. 1 effective date, Alperstein's son, Andrew, who turned 16 last week, is not covered.

Virginia drivers also face some changes beginning tomorrow, when the state will begin renewing licenses every five years rather than every four.

Once the state's 3.8 million drivers are phased into the system, licenses will be renewed when drivers reach an age that ends in either five or zero. The legislation mandating the new system also raised the yearly license fee from $2.25 to $2.40.

Other laws taking effect on Jan. 1 in Maryland will require all physicians to report adverse reactions to pertussis, or whooping cough, vaccine, and permit the state Racing Commission to draw up a telephone betting system for horse racing.

Maryland's saltwater fishing license law was part of a package of bills introduced by Gov. Harry Hughes in an effort to begin the restoration of water quality in the Chesapeake Bay. License proceeds will be used to increase sportfish stocks.

The rockfish ban, which does not require legislative approval, will prohibit both commercial and sportfishing for the state fish, and will last a minimum of four years.