Metro General Manager Richard S. Page, responding to a new report on the Jan. 13 subway accident that crumpled an aluminium-sided rail car against a concrete pillar and killed three people, yesterday ordered a reassessment of the "crash worthiness" of Metro's 300 cars.

Page said Metro would study modifying the thin-skinned rail cars to make them more collision-resistant and altering the design of 300 other cars it has ordered. But he said that such changes might not be a practical way to improve safety.

Cars now in use are reinforced in the front and rear but their sides and roofs are sheets of aluminium. "The cars are not basically designed for a side crash. They're designed for head-on" collisions, which in most rail systems are far more common, said assistant general manager John Egbert.

However, the only two significant collisions in Metrorail's history have both involved side hits--the January accident and a test train collision in 1977.

In ordering the crash-worthiness study, Page was following a suggestion contained in an internal Metro accident report released yesterday.

The Jan. 13 accident occurred when a packed car derailed and was dragged against a concrete pillar between the Smithsonian and Federal Triangle stations. Parts of the car's floor and roof collapsed and seats were crushed, leading to suggestions that they were too flimsy.

Metro officials said that most rail transit experts believe side collisions are rare and that heavy steel reinforcement to guard against them could raise purchase price and weight, making the cars impractical to own and operate. Metro's focus, instead, is to prevent collisions though modern equipment such as switches and automatic train control.

The report also noted that when the train derailed, emergency electrical power failed in all of its six cars, plunging riders into darkness. Page announced yesterday that Metro would make any changes needed to assure power would not fail again.

The report recommended that cars be equipped with devices that record on a continuous loop of tape such data as electronic speed commands and positions of doors as a car moves along the tracks. The tapes would be useful in maintenance and in investigations of any future accidents, it said. Page said Metro would study the idea.

Page endorsed recommendations to give the 1,200 employes who work in the system every day better training on how to react during emergencies and to conduct frequent joint training between personnel from Metrorail's control room and local fire departments. The study credited rescue workers with a "remarkable and commendable" response to the Jan. 13 accident.

The Metro committee's report was released simultaneously with the final report of a separate investigation by the American Public Transit Association. Both underlined earlier findings that repeated errors were committed by the train's operator, a supervisor at the crash site and people in the central control room and that Metro training and procedures were deficient.

Page said that Metro has already made numerous changes to correct shortcomings uncovered after the accident and that Metrorail is safe.

In other developments:

Page said labor-management talks have made major progress toward settling a six-month-old strike at a Pennsylvania brake factory that is delaying production of rail cars and forcing Metro to push back opening dates for new stations. The factory's "management is now beginning to plan for resumption of work," Page said.

However, a spokesman for the union leading the strike at Westinghouse Air Brake, a division of the conglomerate American Standard Inc., said that many difficult issues remain to be settled. A company spokesman declined comment.

Metro has already pushed back by seven months the projected opening date of the next segments, the Yellow Line shuttle between Gallery Place and National Airport and the Blue Line extension to Huntington. The new date is summer 1984, but opening could be later than that.

The Metro board approved a $62 million capital program for bus rehabilitation and garages, subject to obtaining federal funds. It includes $14 million to build a new garage in Landover and $7 million to renovate an existing garage on upper 14th Street in the District.