Federal safety officials blamed the captain of USAir Flight 5050 yesterday for the cockpit confusion that caused the aircraft to skid off a La Guardia Airport runway into the East River last year, killing two of the 63 people on board.

Capt. Michael Martin failed to notice that the aircraft's rudder was mispositioned for takeoff, lost track of the plane's speed as it hurtled down the runway and became confused about who was steering the Boeing 737-400 as he struggled to abort the takeoff, the National Transportation Safety Board (NTSB) found in a nine-month investigation.

As a result, the plane careened off the rain-slicked runway and crashed onto a lighting stanchion, breaking into three pieces at 11:21 p.m. on Sept. 20. Two passengers were killed by the impact. The rest poured into the dark and chilly waters, some unable to swim and some pulled under the runway deck by the current.

"I think the record demonstrates {Martin} was weak," safety board member John K. Lauber said. "There were so many lapses."

Martin's errors began with his decision to allow the first officer, Constantine Kleissas, to handle the takeoff, safety board members said. "Both pilots were relatively inexperienced," the board report said, but it was Kleissas's first takeoff in the aircraft as an unsupervised pilot. He had not flown for 39 days. He and Martin were flying together for the first time, and it had been a rainy, foggy night.

The safety board recommended that the Federal Aviation Administration expedite the work of a government-industry task force studying whether to prohibit pairing inexperienced pilots. The safety board recommended such a rule after the crash of a Continental Airlines jet in Denver in 1987.

Since last year, USAir has tightened its crew-pairing rules in ways that would prevent a reccurrence of Flight 5050's cockpit combination, said senior vice president Patricia A. Goldman, a former safety board member.

Martin could not be reached for comment, but the Air Line Pilots Association (ALPA) said the board's conclusion blaming the pilot was "an absolute travesty." ALPA spokesman Thomas J. Kreamer said, "We just totally disagree."

Kreamer said the board should have paid more attention to problems with the design of the aircraft's rudder trim system, specifically the knob in the cockpit that holds the rudder in position. The rudder is a vertical surface on the tail that causes the plane to move right or left.

The USAir plane pushed back from the gate with the rudder trim knob in the full left position, which caused it to veer to the left as it taxied and began its takeoff roll. A plane can take off and fly with such a problem if the pilot compensates by pushing on the foot pedals that also control the rudder. One sign of a full rudder trim is that it moves the foot pedals 4.25 inches out of their normal position. Investigators said the captain should have noticed these signs before the takeoff.

Since the accident, at least 90 instances of misplaced rudder trim knobs have been reported, safety board investigators said.

"We don't think the design of the rudder control knob had anything to do" with the cause of the accident, said safety board chairman James L. Kolstad.

The board was more concerned by chaos in the cockpit apparent during the hectic 54 seconds between the beginning of the takeoff roll and the moment the plane crashed into the water. At one point, "nobody was steering the aircraft," said safety board investigator Robert Benzon.

Martin and Kleissas are still flying as USAir pilots, although Martin has been demoted to a first officer and has completed a retraining course, Goldman of USAir said.