Even if everything goes splendidly, it will be the middle of March at the earliest before Metro patrons can stop holding their ears to muffle the shriek of the subway brakes.

That date is derived from a deadline top Metro officials set for themselves at a Metro board committee meeting yesterday. They promised the committee that a testing program of various temporary solutions to the brake problem will be completed by Feb. 24 and that purchasing of the best solution will begin by the end of February.

Metro is testing several combinations of brake pads and sounddeadening materials for its disc brakes system in hopes of finding one that will reduce the braking noise from levels that have been measured as loud as those of a jackhammer.

However, that will just be the beginning, assistant general managers John S. Egbert and Theodore Weigle told the board members. Metro is looking at the entire design of its brake system to see if major reworking would not be cheaper to maintain and quieter to use.

The present system, officials said, is costing Metro $4 million annually in labor and parts. While it stops the trains safely, a change in the materials used in commercially available brake pads appears to be the culprit in the noise problem, which first became pronounced in November. Metro began experimenting with the brakes months earlier, Egbert said yesterday, with the primary goal being to find a system that would require less maintainance and fewer changes of pads and discs.

Metro's brakes are of unique design and therefore suffer from a problem transit systems seem determined to create for themselves. Because the brakes are unique, there is small market potential for any manufacturer who might wish to invest heavily in research and development.

Metro's disc brakes are hydraulically actuated. Two pistons drive a plate against an outer brake pad, which squeezes against a disc and an inner brake pad. The vibration resulting from that action causes the irritating noise.

Egbert said that a promising new brake system is being tested on some Metro cars. It, too, is a disc system, but squeezes the disc uniformly instead olf unevenly, as happens with the piston system.