SAN DIEGO - Trolley system improvements will result in closures of downtown stations over the next two weekends, but passengers will be able to use buses to get where they are going, Metropolitan Transit System officials announced Wednesday.

Also, rail service will be interrupted along the North County coastline for construction work.

Because workers will be installing new overhead electrical lines, the current wires need to be de-energized, which will affect the entire downtown stretch along C Street, said Wayne Terry, the chief operating officer of the Rail Division of the MTS.

Aging rails and signals will be replaced, and station platforms will be raised 8 inches to accommodate new low-floor trolley cars like the ones used on the Green Line between Old Town and Santee.

Additional work will result in the station at America Plaza, at Kettner Boulevard and Broadway, being closed until January and moved temporarily to C Street. The Seaport Village station will also be shut down until next year, so passengers there will have to access trolleys at the Convention Center.

"It'll be a little painful in the short term, but in the long term there will be a lot to enjoy with the improvements,'' Terry said.

Next June, the MTS plans to run the Green Line all the way to the main station at 12th Street and Imperial Avenue near Petco Park, and some operational changes will lead to faster, more convenient trips, he said.

Terry said the MTS is spending $600 million to bring the improvements to trolley lines. Once downtown infrastructure is completed, the Blue Line, which runs from downtown to the international border, will be next. According to Terry, the Blue Line has the highest ridership of any above-ground light rail line in the U.S.

The Blue Line was built 30 years ago on pre-existing track, which is aging and gives commuters a rough ride in some areas. Work on that line should be completed in two years, Terry said.

Transit officials said weekend riders will see signs that give information about their alternatives, and the closed stations will be staffed by ambassadors and security officers who will provide direction. Also, information will be given on the MTS website -- sdmts.com -- and radio and television announcements.

"Despite all the work going on, we will get all passengers to where they are going,'' Terry said.

In the North County, rail lines will be closed in Carlsbad and Camp Pendleton over the next couple of weekends for improvements.

North County Transit District officials said the Coaster will run normally south of Poinsettia Lane, with buses in points north. They also said Amtrak will put passengers on buses from Irvine-south, and the Metrolink will temporarily suspend service to Oceanside.