Performance of Metro's troubled bus and subway system improved steadily in recent months, according to figures released yesterday. Metro officials cited not only better maintenance and employe skills, but also a factor they can't take credit for--unusually mild weather.

"Most of our vital signs are on the way up," General Manager Richard Page told the Metro board yesterday in presenting a performance report that was part of efforts to monitor service quality more closely.

The number of trips missed due to lack of a driver or roadworthy bus fell from 3,262 in July to 377 in November, according to Metro. In the same period, the percentage of scheduled trips completed rose from 97.8 to 99.1. In November, Metrobuses averaged 1,101 miles between breakdowns that disrupted service, compared to 697 miles in July, the report said.

Performance usually is best when buses and trains are spared extreme temperatures that cause freezing or overheating. This year, Metro officials said, the weather has been more helpful than usual.

The bus performance gains were also attributed to heavy-duty overhauls, better preventive maintenance, an outside contract to rebuild bus engines and success in lowering absenteeism, the report said.

Metrorail also improved, completing 97.8 percent of trips within five minutes of schedule in November, up from 96.8 in July. Average car-miles between service interruptions rose from 8,299 in July to 16,580 in November.

The report said the rail gains were due to mild weather, rail personnel's growing skills in moving disabled trains, and unusually few flooding incidents or outside disruptions, such as suicides. Efforts to reduce breakdowns of trains have not yet had a significant effect, officials said.

Metro officials also reported settlement of three of 21 lawsuits filed against Metro in connection with the Jan. 13, 1982 derailment that killed three people. Forty-nine of 93 claims filed directly with Metro have been closed. Metro has paid settlements totaling $128,000.

The board gave final approval to building the future Wheaton station on the east side of Georgia Avenue south of Reedie Drive, now occupied by the Country Boy produce market.