Air Force F-15 jet fighters intercepted four Soviet bombers over the Alaskan coast just as the Soviets turned toward the Prudhoe Bay oil field, Sen. Frank H. Murkowski (R-Alaska) reported. He said the incident occurred Thursday, but was classified. The Soviet aircraft were 90 miles off northern Alaska when they were intercepted by two F-15s from Galena Air Force Base in central Alaska. Senate Intelligence Committee analysts called the Soviet bomber activity significant, Murkowski said. Although the Air Force sporadically intercepts Soviet planes in the area, this apparently was the first time that four of the bombers flew such a mission together.