Moscow — 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.