Officers opened fire after two men dressed as women refused to stop at the gate to the National Security Agency HQ in the US and then smashed into a police vehicle blocking the road, officials said.
One of the men died in the incident, while a police officer and the other man in the vehicle were injured, the NSA said in a news release.
Investigators have not yet determined how the man in the vehicle died, and the conditions of the wounded man and officer were not immediately clear.
An FBI spokeswoman said earlier in the day that the incident at Fort Meade, Maryland, was not believed to be linked to terrorism.
A senior defence official said the two men were dressed as women.
The NSA is headquartered on a sprawling US Army installation near Baltimore.
The FBI is investigating and working with the US Attorney's Office in Maryland to determine if federal charges are warranted, FBI spokeswoman Amy J Thoreson said.
Local television showed two damaged vehicles near a gate and emergency workers loading an injured uniformed man into an ambulance.
Aerial news images showed that one of the damaged vehicles was a white sports utility vehicle marked "NSA Police". Its front end was crumpled and the bonnet was up. The other was a dark, unmarked SUV.
A building on the NSA campus was damaged by gunfire earlier this month, and authorities captured a man they believe fired that night on the NSA site, as well as earlier at several nearby places and two moving vehicles.
The suspect in that case, Hong Young, told police he heard voices directing him to fire at one of the occupied vehicles.
The gate that serves as the NSA entrance is just off the Baltimore-Washington Parkway, a scenic commuter route.
In addition to the NSA, Fort Meade is home to the Defence Information Systems Agency and the US Cyber Command. About 11,000 military personnel and about 29,000 civilian employees work on the property.