Robert A. Heinlein, who spent a half century writing about man's relation to technology, society and the universe, was remembered upon his death at age 80 as science fiction's prolific "grand master."

"He was probably the best of us all at his peak," Isaac Asimov, one of the top science fiction writers, said Monday. "He forged the route the rest of us followed."His early stories in the 1940s were so far ahead of everything else being done that he made an enduring name for himself as the best science fiction writer."

Heinlein, whose books explored the future while questioning the morals and beliefs of the present, died of heart failure Sunday at his home in this seaside community 130 miles south of San Francisco.

Heinlein suffered for years from emphysema and had undergone numerous operations, including one to relieve restricted blood flow to his brain.

Heinlein, a former aviation engineer, dreamed up the water bed in his 1961 classic "Stranger in a Strange Land," and envisioned an atomic power plant years before the Manhattan Project. The current issue of Books in Print lists 64 books written by Heinlein. More than 40 million copies of his writings have been sold.

He won the Nebula award from the Science Fiction Writers of America in 1975; and an unprecedented four Hugo awards, in 1956 for "Double Star," in 1959 for "Starship Troopers," in 1961 for "Stranger" and in 1966 for "The Moon is a Harsh Mistress."

His other works include "The Green Hills of Earth," "The Man Who Sold the Moon," "Have Space Suit Will Travel," and "Puppet Masters."

"Heinlein wrote about worlds that people believed in," said Lester del Rey, a science fiction writer-publisher reached at a convention in Las Vegas. "He made them seem real and solid, real lived-in worlds. His early work was quite extraordinary that way."

Heinlein's books were written in a spare, matter-of-fact style, but they presented readers with thoughtful questions about how life should be lived.