Metro's balky Farecard machines, a source of exasperation for many subway patrons, have been breaking down more often than before, according to the transit authority.

During the past 20 months, 15 percent of the rail system's 400 vending machines, at which Farecards may be purchased or traded in, were inoperative on an average day.

The breakdown rate climbed to 19.7 percent in April and then dropped to 18.9 percent in May and 14.1 percent last month.

In contrast, about 11 percent of the Farecard vending devices broke down on an average day during the preceding 40 months.

But Metro officials said yesterday that remedies would soon be administered.

"We are trying. We're moving in the right direction," said Joseph P. Greenway, a general superintendent in charge of maintaining the Farecard machines and other electronic equipment.

The transit authority, carrying out plans announced more than a year ago, recently began overhauling the troublesome vending machines, outfitting them with new pulleys, belts and bearings.

The rehabilitation work will probably take 1 1/2 years, Greenway said. By then, Metro hopes to reduce the breakdown rate to 5 percent.

The recent increase in malfunctions was attributed to "equipment fatigue," an affliction brought about by wear and tear and by old age.

Many of the Farecard vending devices are five or six years old, Greenway said, and they badly need to be rejuvenated.

Already, Greenway noted, signs of hope have emerged.

The electronic gates, through which patrons pass after inserting their Farecards, have recently been renovated, and the rate of malfunctions at the gates was a mere 3.2 percent in June.

Moreover, the Addfare machines, which suffer comparatively little wear and tear, had a June failure rate of just 3.9 percent, Greenway said.

Addfare machines are used by passengers if they need to increase the sums shown on their Farecards before going through the exit gates.

As part of the transit agency's efforts to revamp the Farecard system, officials have tested an array of new devices, some of which are considered likely to help reduce fare evasion.

Statistics presented yesterday to a committee set up by Metro's board of directors appeared to bear out previous estimates of substantial losses stemming from misuses of flash passes.

The special discount-rate passes, which may be purchased by transit riders, provide $4 to $6 worth of subway fares during two-week periods.

But many of these passes have been found to be used improperly after two weeks have elapsed.

Metro officials previously estimated that one out of every three or four passes used in the subway system is invalid with losses in fares amounting to $750,000 a year.

Data presented yesterday indicated that nearly half the passes are obsolete and that annual losses might exceed $1 million.