The Air Force, reversing its earlier position, has decided to allow women to become launch control officers for the Minuteman and MX nuclear missiles, though they will not serve on mixed crews with men. Maj. Michael B. Perini, an Air Force spokesman, said the Strategic Air Command had decided to allow qualified women to apply for Minuteman and MX training classes later this year. The first two-woman launch crew could be deployed by the spring of 1986, he added. The Air Force now has about 75 women serving on the four-person launch crews for its Titan missiles, the oldest intercontinental missiles still in service. But the Titan bunkers are large enough to separate the men and women.