Federal Aviation Administrator J. Lynn Helms has decided to prohibit operation of the European-made Airbus A300 wide-bodied aircraft at Washington's National Airport, transportation officials said yesterday.

Eastern Airlines, which operates 25 of the twin-engine airplanes, had hoped to win clearance for the plane for use on its Air-Shuttle between Washington and New York and on routes to Florida.

In a letter to Eastern President Frank Borman, Helms said he had decided that the Airbus couldn't be operated safely into National under all conditions at all times.

Helms' decision reportedly was made after an extensive review of the engineering design data and performance data of the aircraft, particularly as it would operate in bad weather at National, which has short runways. Among other things, Helms was said to be concerned about possible engine failures and the plane's ability to stabilize before landing when using the curving approach to Runway 18 to the south--a runway used for about 45 percent of all arrivals.

Helms, a former test pilot, personally flew the A300 into National several times on Dec. 5 to see for himself how it handled before he made his final decision, transportation officials said.

Eastern officials said yesterday there was an honest disagreement over the technical aspects of the plane's ability at National. "We think the airplane is safe there or we wouldn't have suggested using it there," Borman said. He said Eastern would take Helms' points and, in conjunction with flight test data from Airbus Industrie, "hope to convince him that the airplane is acceptable" at National.

"I think he's basically worried about loss of an engine on a very hot day," Borman said. He added that Eastern would seek to "dispel his concerns" by doing tests with the manufacturer in actual conditions with engines out.

Eastern has been trying for almost four years to get federal approval to use the plane at National. The Miami-based airline brought the Airbus to National in April 1978 to demonstrate to federal and local officials that it would help reduce the noise at National. At that time, FAA Administrator Langhorne Bond said the A300 was the "quietest" jet plane ever to land at National. The plane, built by a European consortium, is powered by quiet-technology General Electric engines.

Helms' decision was made under the FAA's new policy for the Metropolitan Washington Airports, which gives the FAA administrator the authority for determining whether two-engine or three-engine, wide-body aircraft not currently in regular operation at National could be operated there safely. Federal officials said no other airline has expressed any interest in using the McDonnell Douglas DC10 or the Lockheed L-1011, the other existing three-engine wide-body aircraft, at National. If airlines seek to use those planes at National, Helms said he will evaluate them in the same manner as he did the A300.

Besides the technical aspects of his decision, Helms said he took into consideration how use of the A300 fits into the overall Washington National Airport policy. He also noted that there are no restrictions on the A300 at any other airports it is currently using.

Yesterday, Sen. John Warner (R-Va.) said Helms' decision was further confirmation of the administration's intention to encourage use of Dulles International Airport. "It is a good airplane," Warner said of the A300. "Hopefully, it will be used at Dulles."

Although Helms made no decision on use of the other wide-body aircraft at National, Warner predicted that neither the L-1011 nor the DC10 will win clearance if it is sought. "Both are larger than the A300 and would be subject to the same rigid test requirements," he said. "It's not likely that they would be able to meet the safety requirements."