Investigators said today an air traffic controller at Little Rock airport informed the crew of American Airlines Flight 1420 of rapidly deteriorating weather, including two wind shear alerts on final approach, before the aircraft tried to land and crashed off the end of the runway.

"The level of care we thought was pretty good on the part of the controller," said George Black, a member of the National Transportation Safety Board, briefing reporters on the crash just before midnight Tuesday that took nine lives and injured scores of others.

Black refused to judge the actions of the pilots, one of whom was killed, saying the board is just beginning an investigation. He only pointed out that the captain has the final judgment on whether to land in any conditions. But other sources said the board will necessarily look into whether after 13 1/2 hours on duty, a fatigued crew might have exceeded limits on crosswind landings set by American Airlines.

The plane, a McDonnell Douglas MD-80 with 139 passengers and a crew of six aboard, roared off the end of the runway and broke apart on a light stand, bursting into flames. A violent thunderstorm was just rumbling onto the northwest edge of the airport and crosswinds with gusts up to 51 mph were buffeting the runway as the landing began at the end of a bumpy flight from Dallas-Fort Worth to Little Rock.

Board investigators were reviewing all area radar data in an effort to determine whether the plane was hit at the last minute by something that no radar on the plane or at the airport could see--either a gust front, a blast of air that may precede a thunderstorm, or a microburst, a rapidly moving downdraft that spreads out as it hits the ground and can rob a plane of lift. The Little Rock airport does not have enough traffic to qualify for a Terminal Doppler Weather Radar, which can see both phenomena.

Black also said that data already available show that the storm contained a "Level 6" cell, the most severe on the scale.

According to Black, crew members first told the Little Rock airport control tower that they had the airport in sight and would land without an instrument landing system. However, clouds suddenly obscured the view of the airport, and they switched to an instrument landing.

The Dallas Morning News reported Wednesday that the plane then did a go-around for a second landing attempt. Today, however, sources said the crew actually performed another somewhat similar maneuver that accomplished the same purpose--a "redirected approach," in which the plane made an S-shaped turn to line up with the instrument landing system.

Sources said the controller gave the pilots a series of wind readings that gradually grew worse. About a minute and a half before the crash, the tower said that winds on the airport were from 350 degrees on the 360-degree compass, at 30 knots--about 34 mph--with gusts up to 45 knots, or about 51 mph.

The controller and the pilots discussed the approaching thunderstorm cell after the controller told the pilots their on-board weather radar was better than anything he had in the tower. The pilots told him the storm was "not as close as you think."

An aviation meteorologist, who asked not to be named, noted that the plane's radar could see rain but not rapid movements of air that might precede it. That might have persuaded the crew it had the time to beat the storm in.

The airport did have a Low Level Windshear Alert System, a series of wind sensors around the airport. When these sensors begin reading winds coming from different directions, they issue a wind shear alert. The Little Rock controller did this twice, reporting that wind direction at two sensors varied by 40 degrees.

As the plane approached Runway 4R, toward the north-northeast, winds measured at the tower began shifting to 320 to 330 degrees, more from the northwest than the north. This produced more of a crosswind, which can be dangerous if pilots do not adjust properly.

The American Airlines pilot manual says that pilots should not attempt to land if crosswind gusts exceed 30 knots on dry runways or 20 knots on wet runways. In low-visibility conditions, the limit is further reduced. Investigators will have to determine exactly how the rule applies to this crash.

Sources said skid marks on the runway indicate that the plane landed with its nose pointing slightly to the right of the runway centerline, rather than slightly to the left to compensate for crosswinds. It then drifted right, then back left with its left landing gear skidding through the grass until the plane became airborne again briefly at the slope at the end of the runway. It passed over a road, hit the ground again and slammed into the light stand.

Black said at an evening briefing that marks on the runway indicate that the aircraft's tires were skidding at least partially sideways as it rolled down the runway. He also said that early flight data recorder information indicates that one of the plane's secondary braking systems did not operate during the landing, although it was unclear why or whether it had an effect in the crash.

Black said the plane's spoilers, which are flat plates on the upper edge of the wings, remained stowed rather than pushing up into the wind to help slow the plane and make certain the tires are firmly planted on the runway. However, he and other investigators said it is unclear whether the spoilers were not pre-armed by the crew, as required, to come up automatically on landing or whether some other problem prevented their deployment. One of the things that will cause them to deploy is a spinning nose wheel, and the skid marks raise at least the possibility that the nose wheel did not turn.

The data also show that thrust reversers, which redirect engine thrust to aid in braking, were deployed at least twice by the crew, but the significance of that fact is unclear. Black said investigators hope an interview with the copilot will help clear up the mystery.

In addition to pilot Richard Buschmann, 48, of Naperville, Ill., those killed in the crash, according to the Pulaski County coroner's office, were Arkansans Mary Elizabeth Couch, 68, Havana; James Harrison, 21, Paragould; and Sara Renee "Sue" Gray, 88; Betty Evelyn Ingram, 69; Linda Joyce McLerran, 65; Gordon McLerran, 64, and Judy Thacker, 53, all of Russellville; and Californian Debra Ann Sattari, 38, Concord.

CAPTION: An investigator peers into burned out jetliner at Little Rock National Airport.