Champion over 800 metres at last year's London Olympics in the first major outing of her career, the 16-year-old became only the second woman after Italian world record holder Federica Pellegrini to break four minutes when she claimed the 400 metres freestyle title on Sunday.
Ledecky was second-fastest in Monday's 1,500 metres heats behind Denmark's Lotte Friis and her coach Bruce Gemmell gave little away when asked about her target for Tuesday's final.
"There might be some time goals but we'll keep them to ourselves for now," Gemmell said on the website of swimming governing body FINA (www.fina.org) on Monday.
"She'll get up and she'll race and she'll have fun doing it and grit her teeth and go. Katie swims the way Katie swims, she likes to go out fast and stay that way."
Ledecky's race is the third of five finals on Tuesday.
Lithuanian teenager Ruta Meilutyte goes for gold in the women's 100 metres breaststroke after breaking the world record on Monday and Ledecky's team mate Missy Franklin features in the 100 metres backstroke.
Ryan Lochte, the second-most decorated world championship medallist after U.S. compatriot Michael Phelps, will bid to become the fourth man to win two 200 metres freestyle golds after Germany's Michael Gross, Ian Thorpe of Australia and Phelps.
Matt Grevers, another American, was quickest in Monday's 100 metres back stroke semi-finals and will be looking to deny Frenchmen Camille Lacourt and Jeremy Stravius, who shared the gold in 2011.
- Sports & Recreation
- Federica Pellegrini