WASHINGTON — The Hope Diamond, all 45.5 carats of it, will remain securely guarded here at the Smithsonian National Museum of Natural History. The Japanese giant salamanders of the National Zoo need not worry if the HVAC systems keeping their habitat just right break down — a maintenance crew will be on call.

But many of the other treasures — living and inanimate — that are housed in the Smithsonian’s vast array of museums, research centers and cultural institutions will not have priority in the event that Congress cannot reach a deal to avert a government shutdown on Tuesday. So federally financed institutions are hurrying to come up with contingency plans that they compare to those for a hurricane or a blizzard.

Smithsonian officials are waiting to learn whether a shutdown, which would begin on the first day of the government’s new fiscal year, will delay one of the most significant acquisitions the Museum of Natural History has ever made.

On Oct. 16, the museum is set to receive a rare, nearly intact Tyrannosaurus Rex skeleton, which is on loan for 50 years from a museum in Montana. If the shutdown drags on for weeks, as it did in 1995 and 1996, the 38-foot-long, seven-ton T-Rex may have to stay out West a little longer before making the trip.