A fundamental change in United States policy concerning fishing off American coast will be implemented next Tuesday when the Coast Guard begins enforcement of a new 200-mile limit.

After a United Nations conference on sea laws failed last year to settle the delicate international issue of fishing limits, most North Atlantic countries announced plans to adopt 200-mile limits and the U.S. Congress enacted a Fishery Conservation and Management Act, extending the previous 12-mile American limt to 200 miles.

Britain and other European Common Market countries began enforcing a 200-mile limit in January in a drive to protect their own fishing grounds and economic resources. India recently stretched it ocean rights to 200 miles and Australia has said it will take similar action if the next U.N. sea conference, scheduled for May, reaches no conclusion.

U.S. officials have said this nation will enforce strictly the new limit, which effectively gives Washington control over about 10 per cent of the world's fisheries resources. The new limit gives the U.S. exclusive fisheries management within the zone except for migratory species of tuna.

The Coast Guard commandant, Adm. Owen W. Siler, siad yesterday his service is "ready and accepts the challenge" of the expanded enforcemment role.

A mix of long and medium range aircraft will patrol areas to monitor foreign fishing and report to ships and helicopters. One ship and four former Air Force aircraft will be reactivated and the Coast Guard will buy four new C-130 planes to beef up its enforcement fleet.

Siler told reporters yesterday the new limit means the Coast guard will have 2 million square miles of ocean to monitor on top of the 545,000 square miles now patrolled. Penalties will include fines of up to $50,000 and seizure of ships.

Government officials said foreign nations will pay an estimated $13 million a year for the right to fish within the 200-mile limit, covering the costs of administration and enforcement. They forecast that the new limit would reduce substantially the current annnual catch by citizens of foreign nations of 6-7 billion pounds of fish.

The U.S. catch int he 200-mile zone, currently estimated annually, is expected to increase to 5 billion pounds over the next five years. That would aid the U.S. fishing industry and could lead to lower consumer prices, official aid yesterday.

Secretary of Transportation Brock Adams warned, however, that Congress must act on Monday to approve bilateral agreements with Japan, South Korean, Spain and the EEC on the 200-mile limit. These agreements permit purchases of permits for fishing in the new zone with specified catches.

Similar agreements were ratified earlier with the Soviet Union, Poland, Taiwan, East Germany, Romania and Bulgaria. Negotiations are continuing with Canada and Portugal.