Military action against a Libyan chemical-weapons factory is being discussed by the United States and its allies, President Reagan said in a broadcast interview.

"Well, let me say that's a decision that has not been made yet," Reagan said in the interview, portions of which were shown Wednesday on ABC's World News Tonight."We're in communication with our allies and with NATO forces and all, and we're watching very closely that situation but even if I had made a decision, I couldn't . . ."

Reagan didn't finish the sentence. The full interview by David Brinkley was to be broadcast Thursday night.

Asked whether military action had been discussed with the allies, Reagan said, "We are discussing with them and we want to pin down completely so that there is no question but that that's what is . . . a plant that he is building and one of tremendous size."

The president said the United States knows the factory's location.

According to a report in The Washington Post, intelligence sources say the factory is in a large complex 35 miles southwest of Tripoli. The complex reportedly includes a plant that is intended to produce aerial bombs and canisters to carry poisonous gas.

The sources also said it is guarded by Soviet-made missiles.

A senior administration official told the Post that military action was one of several options that had been discussed, but it "is not under active consideration."

More than 100 countries will represented in Paris on Jan. 7-11 to discuss enforcement of the 1925 Geneva Convention outlawing poison gas and other chemical weapons.

"The thrust of our consultations is to establish what we know about this plant and to raise the issue as a menace to world peace and to make this a major item of consideration at the Jan. 7 conference," a senior official told the Post.