Since the beginning of July, Metro has introduced 43 "bend-in-the-middle" buses to passenger service in the city. But since then, the overwhelming majority of the new buses -- which cost $173,500 each -- have been out of service for varying periods of time because of mechanical problems.

The new buses have become common sights along the Benning Road and Connecticut Avenue routes. However, recurring failure of the air conditioning has converted some of the them into virtual sweat boxes on wheels.

Technically known as "articulated buses," the vehicles were purchased by Metro to save on driver wages. Although the $173,500 price tag of each bus is considerably higher than the $65,000 Metro paid in 1976 for a conventional bus, the elongated buses can carry up to 85 seated and standing passengers, 29 percent more than a conventional bus.

The air conditioning problems on the vehicles, however, have irritated many riders.

"(Metro) may be saving money, but what's the use of saving on bus drivers when they're giving poor service," said James Wilson a Northeast resident who regularly rides the new buses on Benning Road.

Since July 9, about the time temperatures and humidity levels began to rise, 40 of the buses have been taken out of service at various times for repairs to the air conditioning system, according to Phil Price, general superintendent of bus maintenance at Metro.

"The air conditioning system is a new design, and we are having problems with individual components," said James Currie, Vice president for administration at American Motors General, the U.S. firm which built the buses in a joint venture with the German company of MAN.

The buses' mechanical problems have not caused any reduction in service, Metro officials say, because only 35 of the 43 buses are o ever scheduled for operation at one time. No more than six buses have been in the repair shop on a single day since the air conditioning difficulties first appeared.

The bugs in the system stem largely from recurring failures of an oil pressure switch on the engine that powers the air conditioning.

"It's kind of ironic that (the switch) is a major item causing some of the problems because it is supposed to make the air conditioning system more reliable," said David Smith, marketing manager for bus and rail products at Trane, Inc., a Wisconsin-based air conditioner manufacturer which built the systems for American Motors General.

The air conditioning units carry six-month warranties, and service representatives from American Motors General and Trane promised, during meetings last week with Metro officials, to expedite delivery of spare parts, Price said this week.

Although the windows of the elongated buses are not supposed to be opened except in emergencies, many riders have taken to opening the windows to get relief from the intense heat that builds up when the air conditioning fails.

"On the hottest days, it stinks on these buses," grumbled Jerry Mooney, a student at the University of the District of Columbia, as he rode to his Southeast Washington home last week."If it's against the law to smoke a cigarette on here, it should be against the law to operate a bus under these conditions."

From the perspective of the drivers, the elongated buses offer some advantages in maneuverability, according to Metro spokesman Marilyn Dicus. The buses' shorter wheelbase makes it easier to turn a corner, and the bendable feature of the vehicles aids visibility.

And the bus drivers also must cope with the high temperatures caused by the air conditioning problems.

"These are miserable riding conditions for the passenger," said Stanley Watkins, 26, who has a driver with Metro for three years. "it's bad for me, but it's even worse for the people who ride them. I get paid at least."

Other mechanical problems have developed on the buses. The automatic rear doors often open and shut repeatedly until the rubber padding on each door is aligned properly.

"We've had some passengers injured in those doors," said Dick Reese, Metro bus equipment engineer. Reese said Metro is redesigning the guard rails to prevent passengers from getting caught in the rear doors when the doors do not close properly.

Reese also cited a problem with the temperatures switches on the electric fan motors attached to the main engine of the buses. Temperatures switch failures sometimes cause overheating of the main engine. CAPTION: Picture 1, A new bend-in-the-middle Metrobus rounds Jackson Place at H Street. By Douglas Chevalier -- The Washington Post; Picture 2, Interior of new Metrobus: more window area, more passenger space. By Douglas Chevalier -- The Washington Post