In the wake of an announcement that Lloyds of London will be canceling war-risk insurance for ships "navigating to Argentina and South Atlantic waters," two major U.S. marine underwriters issued similar notices yesterday and others were meeting to decide whether to follow suit.

As of tonight, ship owners insured by Lloyds, the American International Marine Agency and Highlands Insurance Co. are giving policy holders 14 days' notice of war-risk insurance cancellation. This applies only to the vessels, not their cargoes.

At the end of the notice period, war-risk coverage will be reinstated automatically outside the excluded waters, "including waters within 200 miles of the Falkland Islands and dependencies." Uruguayan waters were excepted. But, in a manner that is followed in other zones, such as the Persian Gulf and the Gulf of Aqaba, coverage within the area would have to be renegotiated.

The financial impact of these moves was difficult to determine. Richard Goodwin, vice president of AIMA, which he said was the largest independent marketer of such insurance in the United States, noted that few of his hull interests were in the area. Also, a higher rate might not be instituted if the Anglo-Argentine confrontation over the Falkland Islands was cooling down.

In New York, the American Hull Insurance Syndicate, representative of 60 companies that write insurance for heavy cargo ships, and the American Institute of Marine Underwriters were monitoring developments and discussing whether to issue a cancellation notice yesterday evening.

According to Alan Huber, a vice president at the Johnson and Higgins insurance brokerage firm in New York, the notice of war-risk cancellation near Argentina brings this procedure into play: A ship will notify its insurer 48 hours before entering exluded waters; before a new war-risk rate can be quoted, the insurer will ask to know the name of the vessel, its flag, ownership, value, destination, the port where it began its voyage, its exact route, the type of cargo it carries and whether the cargo is being imported or exported.

On the basis of this information, a rate will be quoted that will stay in effect for seven days and then need to be renegotiated. Even if a ship plies the excluded waters for only one hour, the seven-day rate applies.

Normal war-risk insurance rates are 2.5 cents per $100 value. Observers envisioned a rise to about 15 cents. Cargo ships serving Buenos Aires tend to be in the $4 million to $6 million category, AIMA's Goodwin said.

"Somehow, somewhere, they make it up," said a marine insurance writer who declined to be named. He said shippers or consignees would likely bear the extra costs.

But James T. Crowley, vice president for marketing, noted that with the 48-hour arrangement, "If you want to ship some freight and it has already left , I can't put a surcharge on it." Still, he did not expect the increased cost to be "back-breaking."

Until Tuesday, some shippers to Argentina had canceled shipments or asked to reroute their cargo overland from Brazil or from feeder ships in Montevideo, Uruguay, but steamship lines were reported keeping to their schedules.

U.S. exports to Argentina already were suffering from devaluations of the Argentine peso last year and last week, making foreign goods more expensive for Argentines, and from limitations the Argentine government had imposed on import licenses and use of foreign exchange.

In the first quarter of last year, U.S. exports to Argentina were valued at $776.4 million, according to the Commerce Department. For the same period this year, the figure is $458.1 million.

"We've had literally hundreds and hundreds of phone calls since April 30 when the United States imposed sanctions on trade with Argentina ," said Walter Bastian, who follows Argentina for Commerce. "Most are from U.S. exporters that have questions on sanctions, on payment; in some cases they're looking for any actions taken by the Argentine government that might affect exports, safety of U.S. personnel."

Asked if Moore McCormack cargo ships were encountering any difficulties as a result of the Falklands crisis, Crowley, vice president formarketing, said, "Malvinas! Please! We have a ship heading to Buenos Aires."He said the first ship feeling the full brunt of the conflict was the Mormacdraco, heading now for Miami and scheduled to arrive in Buenos Aires June 1.