Adam B. Ulam, Gurney professor of history and political science emeritus and a world-renowned expert on the history of the Soviet Union, died of lung cancer Tuesday at Youville Hospital in Cambridge. He was 77.

Ulam served as director of Harvard's Russian Research Center from 1973 to 1976 and from 1980 to 1992. A prolific writer, his works included The Bolsheviks and Stalin: The Man and His Era, considered by academics to be among the most important profiles of Lenin and Stalin, respectively.

A member of a wealthy Jewish family, Ulam was born in Lvov, Poland in 1922 and lived there until age 16.

In August of 1939, Ulam's father insisted that he and his brother flee Poland for fear of Hitler. Days later, Germany invaded Poland.

According to Ulam's ex-wife, Mary Burgwin Ulam, his was the last boat to leave Poland for America before the attack.

In the U.S., Ulam's brother Stanislaw held a junior fellowship at Harvard and used his salary to support them.

"Stan supported Adam," Burgwin Ulam said. "It was hard because there was little money."

Stanislaw Ulam, a mathematician who helped build the hydrogen bomb, initially supported Ulam at Brown University.

"Adam was an outstanding scholar," Burgwin Ulam said. "He [eventually] won a scholarship, and Stan didn't have to pay anymore.'

After Brown, Ulam received a Ph.D. in government from Harvard in 1947 and taught until his retirement in 1992.

Before his death, Ulam wrote an autobiography that Burgwin Ulam said will be published in late spring. The first chapter is available online at www.aulam.org.

Baird Research Professor of History Richard Pipes, who has worked closely with Ulam at the Russian Research Center for 50 years, described Ulam as "amusing" and "a very witty man" who told jokes and rarely discussed work.

"You wouldn't know he was working until his books came out," Pipes said.

But he said Ulam made significant contributions in his field.

"He took available information and recast it in an intelligent and interesting way," Pipes said.

A close friend of the family called Ulam an "imposing presence."

"One felt the weight of his erudition," she said.

But despite his imposing appearance, he had a softer side--"he wept over the death of our dog," Burgwin Ulam said.

Ulam was also an avid sports fan--a tennis player and Red Sox devotee.

"He will be buried in the Harvard plot [in Mount Auburn cemetery] overlooking Harvard Stadium, which he would love," Burgwin Ulam said.

Ulam is survived by his ex-wife and his sons, Alexander and Joseph Ulam.

According to Burgwin Ulam, despite their divorce, a sense of "deep love" pervaded their family life. She said she and her ex-husband had planned to re-marry.

A memorial service for Ulam will be held today at noon at Mount Auburn Cemetery.