Citing "bad skills" among mechanics, failing transmissions and aging buses, senior managers of the Metrobus system called on the Metro board yesterday to approve costly new programs to improve bus reliability.

Without action, operations chief Theodore Weigle told the board's budget committee, "We're going to continue to be mired down in the kind of problems we have . . . . I think we're in the year of tough choices."

Reliability has declined in recent years to the point that the 1,600 buses in Metro's rush hour fleet averaged less than 1,000 miles between breakdowns last fiscal year.

Metrobus chief Tom Black proposed specific reliability targets for the next five years. Though he gave no estimates of the cost of achieving them, they would clearly require major new spending. The proposal comes at a time when board members are anxious to improve reliability but are under heavy pressure from area governments to keep the lid on subsidies.

Metro already has taken short-term steps, such as rebuilding engines and transmissions. According to the staff paper, Metro should continue the job by:

* Improving maintenance. Metrobuses tend to be fixed only when they break down, officials say.

* Establishing a formal certification program and more rigorous training for mechanics.

* Hiring more mechanics. Metrobus managers for years have said garages are inadequately staffed.

* Establishing an inspection program to assure the quality of maintenance work and a management information system.