Metro took the first step yesterday toward running eight-car trains when its directors gave initial approval to a $236 million upgrade of the subway's electrical power.

Transit officials said they needed to improve 44 of Metro's 93 electric substations, which are scattered throughout the 103-mile railroad. The substations, many of which are 30 years old, convert electricity that comes from power companies into current to run the trains.

The subway has to increase the amount of electricity it can draw to power the longer trains, which are key to Metro's plan to ease crowding. An eight-car train can carry 200 more people than a six-car train, which is the longest train Metro now operates.

"This is something we have to do," said T. Dana Kaufmann, who represents Fairfax County on the Metro board. "We have to be looking 10 years ahead on everything we do."

In addition to upgrading the power system, Metro plans to buy an additional 120 rail cars, which would allow it to lengthen about one-third of its trains to eight cars by 2008. That means the subway would be able to carry 30,000 more riders during peak travel hours, planners say.

But the $229 million purchase of 120 rail cars and the $236 million power upgrade both depend upon the agreement of local governments to give $1.5 billion to Metro over the next six years.

The plan, known as "Metro Matters," has approval from Maryland, Arlington and Alexandria but still needs a commitment from the District and Fairfax County, Metro officials said. Transit officials said they need all the governments to endorse the plan by Oct. 21 to order the first wave of new rail cars at a discounted price.

Metro board member Jim Graham, who serves on the D.C. Council, said District officials have not endorsed the Metro Matters plan because they are concerned that it assumes $260 million in federal funding without a commitment from federal officials.

Metro was built to operate eight-car trains, but it has never had enough rail cars to run trains that long. Instead, it operates a mix of four- and six-car trains. The subway's rail cars are designed to operate in married pairs, so the number of rail cars in a Metro train is always an even number.

In addition to paying for new rail cars and upgraded power systems, the Metro Matters plan calls for the purchase of 185 buses to alleviate crowding on popular routes.

More people rode Metrorail in the past year than in any year since the subway opened in 1976, at one point breaking the record for single-day ridership. Average weekday ridership was 652,578 on the trains and 502,971 on the buses.