Soviet Union warns that it would develop its own MX

Soviet Defense Minister Dmitri F. Ustinov warned the United States that if it deployed the new MX missile, Moscow would respond by developing a similar weapon of its own.

''If the present leadership of the White House . . . challenges us by beginning the deployment of the MX missile (yet to be approved in Congress), then the Soviet Union will respond to this by developing a new intercontinental ballistic missile of the same class, and its characteristics will in no way be inferior to the MX,'' Mr. Ustinov said.