Widely considered a military hawk, President Richard M. Nixon fretted privately over the notion of any no-holds-barred nuclear war, newly released documents from his time at the White House reveal.

The recently declassified papers, from the first days of the Nixon presidency in 1969 until the end of 1974, show that Nixon wanted an alternative to the option of full-scale nuclear war - a plan for a gentler war, one that could ultimately vanquish the Soviet Union while avoiding the worst-case situation.

The papers provided a glimpse behind the scenes at efforts to find choices other than "the horror option," as the national security adviser, Henry A. Kissinger, called the worst-case scripts for all-out nuclear war that were then in place.

Qualms about causing so much death were hardly the only motivation. American officials worried that their nuclear threat lacked credibility because it was so awful that adversaries questioned whether the United States would ever use it.

In a 1969 diary entry, Nixon's chief of staff, H. R. Haldeman, recalled the president's taking part in an exercise that day aboard the Boeing 707 outfitted to conduct nuclear warfare from the air.

"It was pretty scary," Mr. Haldeman wrote. The president asked many questions about "kill results," he wrote, adding about his boss: "Obviously worries about the lightly tossed-about millions of deaths."