THE TWO AMERICANS on the International Olympic Committee said Monday that they believe there is no chance the full committee will vote to move next summer's Games from Moscow or to postpone or cancel them. The complications for the committee are too great. If the two men, Douglas F. Roby and Julian K. Roosevelt, are right, it is time to start planning a substitute.

The athletes, from the United States and other countries, who will probably not be going to Moscow deserve this much. They have trained hard for months, or years.If the test of the Olympics is now to be denied them, the best possible alternative for Moscow's Games should be found. It should not be just another national sports festival in Colorado Springs, the substitute the U.S. Olympic Committee appears to have in mind. It should be a real sports extravaganza run, preferably, by the Olympic Committee, or, if that is not possible, by an ad hoc committee drawn from the AAU, and NCAA and the other groups that supervise amateur athletics.

The elements of such an enterprise are readily defined. It should encompass, if possible, all of the sports and events included in the regular Olympics. It should be open to world-class athletes from everywhere, whether or not they compete in Moscow. And it should have as much prestige and publicity as the sponsoring nations can give it. There is not enough time before summer to put together a full-dress substitute, given all the embellishments the Games enjoy. But there is time to put together -- in one city of several -- the athletic competitions that are the essence of the Olympics.

What is needed first is agreement among athletic officials and political leaders that such an enterprise should be undertaken and -- then an -- an all-out effort to make to work. What is wanting now are the commitment and the energy. It is understandable that the USOC is reluctant to meet this challenge. It has rules and procedures to follow, not to mention the chore of supervising the winter Olympics in Lake Placid next month and preparing for the 1984 Games. But surely the organizational ability exists elsewhere in the sports world -- here and abroad -- to put on in, say August an Olympic-size track meet, volleyball tournament, equestrian competition and so on. And surely there are cities and institutions -- here and abroad -- that could make available the facilities for such events. Gribbs ruled that the couple's plan would violate a Michigan law on adop