Metro's maintenance director yesterday told the men who designed the subway over the last decade that they had created a system that was too costly and difficult to maintain.

Ralph Smith, director of Metro's office of general maintenance, declined to put a dollar value on Metro mistakes. But the proposed operating budget for his department alone for the next fiscal year accounts for the biggest single proposed manpower increase in Metro and a dollar increase of $6.6 million.

Smith said the biggest maintenance problems were caused by the fact that Metro's stations and tunnels leak more than they should, causing water to collect in places where it doesn't belong, and by the fact that track is wearing out more rapidly than anticipated -- particularly on curves and in switches.

Further, he said, lights are located in places that make bulbs and tubes difficult to replace: the tiles in the floors of the station tend to crack and break, requiring repalcement, because of the type of bed on which they are installed.

The cumulative cost of these and other problems will be hundreds of millions of dollars over a period of years, Metro officials said in interviews.

Smith made his plea at a special day-long meeting of the more than 60 design firms that worked on the first 10 years and 60 miles of Metro subway contracts. The specific purpose of the meeting, according to Metro's design and engineering chief, John Egbert, was to underline problems that have developed over the years and see if better construction methods can be applied in the future.

The problems with maintenance have been discovered only since the first Metro segment opened in March 1976. Lessons learned can be applied to some of the 26 miles still under construction or the 40 miles still to be put out for contract. Thirty-four Metro miles will be operating with the opening of the Orange Line to Ballston in Arlington County on Dec. 1.

"The best maintenance cannot do much when an item is difficult to maintain," Smith told designers from some of the top engineering design firms in the United States. The Metro system, he said, "should not require unusual worker skill, unusual numbers of people or rare pieces of equipment."

In an interview afterward, Smith said that he believed Metro has developed a solution to the problem of track wear, and that the design and engineering people agree with the solution. Guard rails will be installed on some curves to reduce the pressure -- and thus the wear -- at the point.

The leaks, he said, have not been solved. Regular Metro riders know of stations where leaks are stopped for a while, then start again, elsewhere. Federal Center SW, Federal Triangle, Metro Center and Pentagon city to name a few stations, have all had visible leaks. Water from those leaks seeps into electrical wiring and electronic control rooms adjacent to the station platforms.

Ed Waddell, Metro's acting director of construction, said specifications for watertight stations have been strengthened since the opening of the Blue Line exposed the leaks to public view, and that construction inspectors are now putting heavy emphasis on watertight construction.

Adding to the maintenance problems, Metro General Manager Richard S. Page said in his budget message to the board recently, has been the fact that some Metro maintenance has been deferred as a cost-cutting device in recent years. The time has come to pay the piper, Smith said yesterday.