TOKYO—Japan’s ruling party called for the nation to develop its own aircraft carrier and buy American F-35B fighter jets in response to what it described as aggressive Chinese actions.

Tuesday’s proposal from the Liberal Democratic Party’s defense panel, if adopted, would be the latest step by the government of Prime Minister Shinzo Abe to beef up defense of outlying islands, including those also claimed by Beijing. In the eyes of China and Mr. Abe’s opponents at home, it would also be a worrying further step away from the...