The MTA’s FASTRACK program — which shuts down huge subway stretches for overnight repair work — has saved $5 million in the first four months of 2012, officials said yesterday.

Now, the MTA plans to expand the program to Washington Heights and the outer boroughs.

Soon A trains from 168th Street to 207th Street, D trains from 161st Street to 205th Street, and E, F, M and R trains from Roosevelt Avenue to Court Square will be shuttered for four consecutive weeknights.

The Lexington Avenue line also will be affected from 42nd Street to 100th Street.