The United States and other major maritime nations have agreed to a new set of standards to reduce the risk of ocean-fouling spills by oil tankers and to increase the safety of life at sea.

The agreement, reached at a 62-nation conference in London earlier this month, will require new equipment and operating systems on both old and new vessels. Deputy Transporation Secretary Alan Butchman said yesterday the new regulations will be fully effective in five years for U.S. ships and foreign ships entering U.S. waters.

Butchman, chief U.S. negotiator at the conference, said the cost of the new standards has not been determined. Whatever that cost is, it can be expected to be felt in energy costs here, since it will increase the cost of getting fuel from the Middle East to refineries here.

President Carter last March called for an international conference on oil tanker safety in the wake of a highly publicized series of oil spills in or near U.S. waters the previous year. By one estimate, 19 tankers carrying 1.1 million tons of oil were lost in 1976.

At a briefing yesterday, Butchman said the two agreements negotiated in London satisfy most of the proposals Carter made in his March statement.

"I think the internatonal organization has responded very well in a short time," he told reporters. "We didn't get everything we wanted . . . but we have really comes a long way, and done it in a way that will protect the world's oceans, and not just our own shores."

Experts estimate that 85 percent of the oil spilled into the world's water-ways comes not from accidents but from "operational discharge," a term that refers to the almost universal practice of using water to wash out the waxy residue in tanks in which oil is carried, then dumping the slimy mixture of oil and water overboard.

Under the agreements, new and existing carriers of crude oil will be required to employ a new technology known as clean oil washing. With that technique, a crude oil is used to wash out the tanks, yielding greater cleanliness, more oil and reduced waste product.

As a safety measure, new and old carriers of both crude oil and the final product will be required to use inert gas systems, which pump nonflammable gases into the tanks being emptied to reduce the amount of oxygen in the tanks and thus cut down the chance of explosions.

The major Carter proposal the conference did not agree to was a suggestion that new tankers be fitted with double bottoms to provide additional protection in the case of groundings.

In its place, the conference agreed to require segregated ballast tanks, located in such a way that they will protect tankers from both groundings and collisions with other ships. A segregated ballast tank is a tank loaded with water to provide added weight and stability for the ship.

Butchman called the ballast tonk agreement "the best solution we could possibly get."

Sen. Warren G. Magnuson (D-Wash.) has introduced legislation to require double bottoms on tankers. A spokesman said yesterday that Magnuson's Senate Commerce Committee is studying the agreement to see if it provides the same level of safety the bill does.

Rear Adm. William M. Benkert, head of the Coast Guard's safety office, said the agreements will likely force the retirement of some "marginal" ships. The tanker market is now seriously glutted, and shipowners would welcome fewer tankers.