A Pan American World Airways jetliner came within about 50 feet of a DC3 cargo plane during an approach to the St. Croix airport in the U.S. Virgin Islands Tuesday, officials said yesterday.

The Pan Am pilot was told by air traffic controllers in San Juan, Puerto Rico, of traffic near him, but could not find the Caribe Air cargo plane because it had no lights, according to a report filed by the unidentified pilot.

The incident at 9:02 p.m. Tuesday involved Pan Am Flight 429, a Boeing 727 with 54 passengers and seven crew members flying from Miami to St. Thomas, Virgin Islands, with an intermediate stop at St. Croix, said Pan Am spokeswoman Pamela Hanlon.

According to officials, the Pan Am plane was on its final approach and was believed to be at about 800 feet altitude when the pilot turned on his landing lights and noticed the other plane.

He abruptly broke off his approach and pulled the nose of his plane up while veering to the left to avoid a collision, officials said. Hanlon said the plane later landed safely at St. Croix.

According to the pilot report, the two planes came within 50 to 100 feet of each other. One source, asking to remain anonymous, said the separation might have been less than 50 feet and that the tail of the DC3 may have come close to striking the Boeing 727's landing gear.

An FAA official said the controller handling the Pan Am plane advised the pilot that radar showed two other aircraft in his vicinity and that the pilot sighted a distant plane but could not locate the other one.

When the crew turned on the Boeing 727's landing lights, the pilots suddenly saw the other plane coming near them.