(FORTUNE Magazine) – Motion picture studios always have a lot riding on their summer releases, and this year is no different. For investors interested in studio action, what follows is a preview of some of the potential boffos and bombs, in approximate order of release: -- Rambo III (Tri-Star). Sylvester Stallone does what the Carter Administration failed to do: take on the Soviets in Afghanistan. But on two counts, his timing is off. The Soviets will be pulling out of Afghanistan by the time the picture opens, and Rambomania may have run its course. The movie, budgeted for around $30 million, is supposed to have cost more than $50 million. -- Willow (MGM) and Crocodile Dundee II (Paramount). The first, a George Lucas-Ron Howard fantasy, also said to have cost $50 million, could be the Star Wars of the 1980s. Or it could bomb like Lucas's Howard the Duck. The second, at $14 million, is the successor to Croc I, the world's top-grossing / film in 1986. -- Who Framed Roger Rabbit? (Disney). This blend of animation and live action is ''very big-budget, very interesting, and very risky,'' according to an executive at a rival studio. -- Coming to America (Paramount). The only way to think about this film is that it stars Eddie Murphy. Says Jonathan Krane, head of a talent and production company: ''With Murphy, you know it has got to be a huge smash.'' -- Vibes (Columbia). The studio that brought you Ishtar and Leonard Part VI could use a hit, and the Cyndi Lauper-Jeff Goldblum comedy should be a modest one.