The National Transportation Safety Board ruled yesterday that an American Airlines pilot made the wrong decision and thus crashed his jetliner at St. Thomas, Virgin Islands, last April. Thirty-seven people died in the crash.

But while the board blamed the pilot, it also said that his actions immediately prior to the crash were ones "his experience would lead him to believe" were proper. According to the board, Capt. Arthur J. Bujnowski, who survived along with 51 others on board, had made 154 landings on the same runaway.

The runaway at Harry S. Truman Airport on St. Thomas Island has been controversial for years. It is very short by jet standards, with a usable length of 5,158 feet, just under a mile long. (Runaways at Dullas International Airport are about two miles long.) Two hills stand immediately at one end of the runaway. The other end is at the Caribbean Sea. All approaches by air are from the sea.

The Federal Aviation Administration has worried about it in official statements. In a 1972 report, an FAA official wrote that "while the airport may be considered safe from a regulatory standpoint, it is a marginal airport and potential for disaster is much higher than most other airports in the region."

After years of local political wrangling and after the crash, the Virgin Islands Port Authority started a $52 million revamping of the airport. Included is a lengthening of the runway by 2,400 feet and the lowering of the two hills at one end of the runway. The FAA has granted $37 million to aid he project.

The safety board in studying the April crash, concluded "that the airport, although less than ideal, is safe" for jets, provided such operations "are conducted within prescribed procedures."

American Airlines Flight 625, from John F. Kennedy Airport in New York, had a normal flight into St. Thomas until it reached the point on the runway where 727 jetliners usually touch down. At that instant, the plane encountered a wind gust that forced the right wing to drop. The pilot made corrections, but the plane continued to float above the runway.

The captain forced the plane to the ground. Then, he told the board, he decided it could not be stopped on the remaining runway. He attempted to take off.

But a jet engine does not "rev up" immediately when power it applied - it takes a few seconds. The captain told the board he could see his plane was not "going anywhere," so he closed the throttles and applied the wheel brakes.

The plane crashed through an antenna site, hit an embankment, became airborne again, destroyed several automobiles parked on a perimeter road and came to rest in a gasoline station. It caught fire immediately.

Some of the firefighting equipment could not reach the plane immediately because of blocked roads and gates, and the firemen who did arrive had left some of the equipment they needed back at the firehouse, the board found.

After the safety board held a public hearing on the crash, the Allied Pilots Association, which represents American pilots, complained in a letter to board Chairman Webster B. Todd Jr. that the history of the airport and the alleged inadequacy of the runway for jets had not been properly examined. There had been two previous jet crashes, but only two fatalities.

Todd, in a telephone interview, said that his staff conducted a "fairly exhaustive analysis" of the airport data after the letter and concluded that the runway was not to blame.

The pilot, the board said, should either have started to take off immediately after encountering the wind gust, or should have continued his attempts to stop the plane after he had forced it to the ground. Either action, the board said, would have prevented the crash.

"Any carrier, pilot group or individual pilot can halt operation into any airport and report to the proper authority any known specific hazard condition," the board said. "The FAA witnesses testified that they were unaware of any such reports before this accident."

An American Airlines spokesman said he had "no argument" with the safety board report.

American is discontinuing jet service into St. Thomas beginning May 1, the spokesman said, while the airport construction project is under way. Instead, jet flights will land at another U.S. Virgin Island, St. Croix, with a propeller connection to St. Thomas.

American has changed some instructions to its flight crews and the FAA has implemented the safety recommendations of the board since the crash, spokesmen said. Capt. Bujnowski is recovering from injuries suffered in the crash and is still employed by American. The other surviving flight crew members have returned to duty, an American spokesman said.