A month after the Dia Art Foundation scrapped its plans to open a museum at the entrance to the High Line, the abandoned elevated railway line that the city is transforming into a public park, the Whitney Museum of American Art has signed on to take its place and build a satellite institution of its own downtown.

The Whitney recently reached a conditional agreement on Wednesday night with the city’s Economic Development Corporation to buy the city-owned site, at Washington and West Streets in the meatpacking district, officials at the museum said yesterday. Plans call for the new museum to be at least twice the size of the Whitney’s home on Madison Avenue at 75th Street, they said, and to be finished within the next five years.