British Airways yesterday grounded its seven Boeing 767-300 jetliners after discovering cracks in the engine pylons, the metal supports that attach the engines to the wings.

John Lampl, a British Airways spokesman in New York, said cracks were discovered Tuesday in one of the planes in a routine visu- al inspection, and later inspec- tions found cracks in five other planes. The airline's remaining 767 was in the air late yesterday on a scheduled flight from Saudi Arabia and was to be inspected on landing.

Lampl termed the cracks "minor." However, a crack in a plane so new is reason for concern.

A Boeing spokesman, Craig Martin, said a Boeing structural engineer is in London to determine how to remedy the problem. Martin said it is unlikely that other 767s are affected, however, because British Airways is the only airline to order 767s with Rolls Royce engines, requiring a different type of pylon from those used with other engines.

All other Boeing 767s use engines made by General Electric or Pratt & Whitney.

"We think there's no reason to believe there's any problem in the rest of the fleet," Martin said.

Bob Buckhorn, a spokesman for the Federal Aviation Administration, said U.S. authorities contemplate no action because the pylon involved is used only by British Airways.

The 767 is one of the world's most modern airliners, first going into service in 1982. The 767-300 is a later version of the jet, powered by two large under-wing engines. The 767 is the second-largest commercial plane made by Boeing, behind the 747, and is somewhat smaller than a McDonnell Douglas DC-10.

The British planes are part of a 17-plane order just now being delivered. Five of the seven planes delivered so far are used mostly on London-to-Paris flights. They have a capacity of 247 passengers. The other two are designated 767-300ER (for extended range) and are used on long-haul flights.

As of July 31, a total of 318 Boeing 767s had been delivered and another 491 were on order. Of those already delivered, 113 are 767-300s or 767-300ERs.