With temperatures already soaring into the 90s, the Metro transit system is girding itself for one of summer's chronic maladies--air conditioners that conk out on packed buses and subway cars.

Though Metro's cooling systems are still considered prone to go kaput, officials have announced new strategies to keep passengers from sweltering.

Air conditioners on buses will undergo extensive daily inspections. A specialist has been appointed to oversee the repairs. Some buses are being overhauled to make sure that their windows will open if cooling systems fail.

"We obviously have no magic new piece of equipment. We haven't invented an air conditioner," said Theodore G. Weigle, Metro's assistant general manager for transit operations. Nevertheless, Weigle and other transit officials expressed hope that the new efforts would pay off.

"We've got to do it better than we've been doing it," Weigle said.

Metro officials surveyed their 1,719 buses one week ago and found that 94 percent of the air conditioners worked. The 6 percent of buses with balky cooling systems immediately were scheduled for repairs.

After several days of hot weather, the Metro bus system started out Monday morning with functioning air conditioners on 86 percent of its buses. Monday evening, a spokesman said, air conditioners were broken down in another 25 to 30 percent of the buses.

It was unclear yesterday how many of these had been repaired by morning.

Like other transit officials, Weigle views such statistics with a touch of resignation. "If we got 60 percent available at 4 o'clock in the afternoon at 90 degrees in the peak hour, we'd be doing very well," he said.

Air conditioners are more likely to go on the blink in the District of Columbia than on buses traveling through Northern Virginia and suburban Maryland, officials say. The District's high breakdown rate is attributed to the number of hours buses are kept on the road without a break and to strains on cooling apparatus caused by frequent stops, starts and overcrowding.

Air conditioners also break down on buses far more often than on subways, partly because the rail cars' cooling systems have a stable power source, electricity drawn from the 750-volt third rail. In contrast, air conditioners in buses are buffeted both by the varying outputs of bus engines and the jolts of driving in stop-and-go traffic.

Even during the hottest summer days, officials say they expect no more than four or five air conditioning failures on subway cars. If one car's cooling system malfunctions, officials say, they may continue to run the train to which it is coupled because each car has a separate air conditioner. They would simply turn off the lights and lock the doors of the lone uncooled car.

Meanwhile, the transit system appears to be nearing the end of one of its longest-running controversies over air conditioning. Amid mounting complaints, Metro agreed in 1979 to buy 151 General Motors Corp. buses with windows designed to remain sealed. It later bought 43 articulated buses, ones that bend in the middle, from M.A.N. Truck & Bus Corp., also with sealed windows.

The sealed windows were intended, in part, to prevent passengers from thwarting the cooling systems by letting in air. The plan quickly ran awry as air conditioners broke down, leaving riders in what were dubbed "steambaths on wheels." Last October, Metro officials agreed to spend $475,000 to get these windows to open.

Yesterday officials said the job was about half done, with the rest of the windows to be unsealed by the end of July.