The Richardson Olmsted Complex is a National Historic Landmark, the highest designation by the United States for historic landmarks. But that alone isn’t enough to make it eligible for all-important federal tax credits, considered essential for rehabilitating historic structures.

For that, an Historic Preservation Certification must be granted by the U.S. Department of the Interior.

A hotel, event and conference space and architecture center are planned for the former state hospital, but concerns about losing the construction season triggered a joint letter from Sen. Charles E. Schumer, Sen. Kirsten E. Gillibrand and Rep. Brian Higgins, urging the federal agency to quickly approve the Richardson Center Corp.’s application.

The letter touts stabilization work and improvements to the buildings and grounds, as well as local community involvement in crafting a redevelopment plan.

“The resulting project is one that will greatly enhance the tourism, recreation and economy of the local community, and help to restore this grand building,” the letter said.

Monica Pellegrino Faix, executive director of the Richardson Olmsted Complex, said the project can ill afford to lose even a month of the summer construction season.

“A number of things that need to line up to get construction going, and to finalize the tax credit investors, could be in jeopardy if we don’t have a decision by early June,” Faix said.

Faix said she was grateful to the State of New York for the “generous” state funding that can be leveraged for the additional tax credit money, and expressed confidence there will be a positive outcome.

“We have done a substantial amount of work with the state historic preservation office, and feel confident we are making wise decisions based on our work with them, and building on all of the preservation research we did,” Faix said.

“We are being very, very sensitive to the historic context, but it is not a perfunctory approval by the Park Service,” she said of the Interior Department’s review.

“They really evaluate carefully to make sure you are adhering by the appropriate standards.”