ATLANTA — Trade ministers for 12 Pacific Rim nations, including the United States and Japan, on Friday neared agreement on an array of differences covering automotive, pharmaceutical and dairy exports, and decided to extend the negotiations into Saturday in hope of concluding the biggest regional pact in history.

The willingness to continue talks, which began in a hotel here on Wednesday, fueled optimism among the participating nations — and apprehension among critics hovering in its halls and monitoring the negotiations from afar — that the elusive Trans-Pacific Partnership was within reach after years of discussion.

Negotiators for the United States and Japan neared a compromise over the length of a phase-out of tariffs on cars and trucks made in Japan and sold in this country.

Yet sticking points persisted, including over compromise language from the American side on protections for drug makers, an issue that stymied previous talks in July in Hawaii.