Former US Democratic senator George McGovern, who galvanized opposition to the Vietnam War only to lose in a landslide presidential election in 1972, has been admitted to a hospice.

McGovern, 90, is best remembered for his lopsidedly failed bid to unseat Republican Richard Nixon as president on a platform urging the withdrawal of US troops from the bitterly divisive war in Vietnam.

McGovern has been admitted to Dougherty Hospice House in Sioux Falls, in his native Midwestern state of South Dakota, Lindsey Meyers, a spokeswoman for Avera McKennan Hospital and University Health Center, said late Monday.

"The family of Senator McGovern wishes to extend their gratitude and appreciation for the many prayers and well wishes and requests complete privacy at this time," Meyers said in a statement.

McGovern was born on July 19, 1922 in Avon, South Dakota.

He enlisted in the US Army Air Corps at the age of 19, flying missions in Europe during World War II, and upon returning home earned a PhD from Northwestern University in 1953.

He served in the US House of Representatives from 1957 to 1961, and as special assistant in charge of the Food for Peace Program under President John F. Kennedy in 1961.

McGovern was first elected to the US Senate the following year, eventually serving three six-year terms, to 1981, and becoming a liberal icon.

From 1998 to 2001 McGovern served as US ambassador to the UN Food and Agricultural Organisation in Rome, and on August 9, 2000 he was awarded the Presidential Medal of Freedom.