TOKYO—Prime Minister Shinzo Abe's ruling Liberal Democratic Party, the only electoral group fully committed to the nuclear power industry, appears set for a landslide win in Sunday's election even though a majority of Japan's voters remain solidly opposed to the continued use of nuclear energy.

In its election manifesto, the LDP is the only political party not calling for the eventual elimination of nuclear power. "We have the responsibility to provide cheap and stable energy," therefore "we will restart reactors...