The National Transportation Safety Board decided yesterday that, for all practical purposes, the Federal Aviation Administration was the probable cause of the World Airways DC10 crash in Boston last January that apparently killed two people.

The board, after two days of deliberations, said the pilot "landed the airplane without sufficient information as to runway conditions on a slippery, ice-covered runway, the condition of which exceeded the airplane's stopping capability."

The pilot did this, the board said, because FAA regulations:

* Do not "provide proper guidance to airport management" on how to measure runway slipperiness in bad weather.

* Do not give the flight crew members the information they need to determine airplane stopping distances on icy runways.

* Do not require that additional factors for snow and ice be included in computations to determine how much runway will be needed to brake to a halt.

The board also said the FAA's air traffic controllers failed to tell the World pilot that earlier flights had reported difficult braking conditions.

The management of Logan International Airport "failed to exercise maximum efforts to assess and improve the conditions of the ice-covered runways to assure continued safety of heavy jet airplane operations," the board said.

The board listed as contributing factors failure of some pilots to report difficult braking conditions in landings that preceded the World flight and the World pilot's decision to land at a computer-recommended speed rather than a lower speed suggested by his manual.

The finding of probable cause is certain to be followed by strong recommendations that the FAA beef up its bad weather regulations. An FAA spokesman said the agency would have no comment until it has studied the full safety board report.