WASHINGTON — An elderly gunman known to authorities as a white supremacist fatally shot a private security guard at the U.S. Holocaust Memorial Museum in downtown Washington yesterday before being wounded by guards who returned fire, officials said.

The security guard, who was identified by police as 39-year-old Stephen Tyrone Johns of Temple Hills, Md., and the gunman were both taken to George Washington University Hospital.

Johns died at the hospital, authorities said later, and the gunman was reported to be in critical condition. A third person suffered minor injuries in the incident, according to police.

President Obama condemned the shooting, which he said underscored the need for vigilance against anti-Semitism.

Museum officials said in a statement that Johns had worked at the museum for six years. They said the museum will be closed today, and lower its flags to half-staff to honor Johns' memory. "There are no words to express our grief," the statement said.

A law enforcement source identified the gunman as James W. von Brunn, 88. On an anti-Semitic Web site he apparently maintains extolling a "Holy Western Empire," von Brunn says he served in the U.S. Navy during World War II, worked for 20 years as an advertising executive and film producer in New York and then became "an artist and author" living in Maryland.

A woman who opened the door at von Brunn's apartment, in a neighborhood outside downtown Annapolis, would not comment.

Some neighbors, who asked that they not be identified, said that they recently invited von Brunn to their home for a drink and that he unexpectedly brought up his belief that the Holocaust did not occur.

"He didn't believe the Holocaust existed. It was just off the wall," one of the neighbors said.

Police recovered a notebook from the gunman that apparently contained a list of Washington locations, law enforcement sources said. Police bomb squads were called to search and secure those locations after the shooting, including one in the 1400 block of Pennsylvania Avenue near the White House.

"Everything is getting checked out," a police source said. No other details on the locations were immediately available.

The FBI sent members of its National Capital Response Squad, SWAT team and Evidence Recovery Team to the Holocaust Museum "to provide on-scene support" after the shooting.

In a statement issued by the White House, Obama praised Johns as "a courageous security guard who stood watch at this place of solemn remembrance."

A spokeswoman for Wackenhut Services Inc. confirmed that the company provides security for the museum.

The museum, the largest U.S. memorial to the Holocaust, was chartered by Congress in 1980 and opened in April 1993. Its permanent exhibit, "The Holocaust," features a self-guided tour with three parts: "Nazi Assault," "Final Solution" and "Last Chapter."

About 400 employees and 300 volunteers work at the museum, which is both publicly and privately funded.