Down First, making its first start in almost a year, came from nowhere to win the American Grand National steelechase today by a length over favored Cafe Prince with Blue Nearco third and Obiwankenobi fourth.

The victory, the first for Mrs. Miles Valentine's 8-year-old bay since the Temple Gwathmey at Belmont Park last fall, was worth the winner's share of the $20,000 put up by the Paul Masson Vineyards for the feature of Foxfield's fall meeting.

"He didn't like the going at all," said rider Doug Small Jr. "We almost dropped out of it on the first turn. . . we were almost 15 lengths behind."

About 1 1/2 miles from home in the two-mile, five-furlong handicap before a crowd of 12,000, "I started hitting him and he finally began to move," added Small, who earlier in the afternoon had won the featured timber race on a very impressive newcomer, Bay Thorne.

It wasn't until the horses were going into the 13th jump that Down First became a factor. By the 14th he was a close-up third and by the 15th he was second to Cafe Prince, the leader since the 11th fence.

Cafe Prince, ridden by John Cushman, still held a three-quarter-length lead at the 16th and final fence but Small brought Down First up on the outside and outran the favorite down the stretch.

Trained by Burly Cocks, currently the nation's top jump trainer, Down First broke down in the Colonial Cup last year and had not raced since. A bay gelding by First Landing-Pocosaba, he won three of five starts in 1979 and won over $25,000 for his owners.