For Kevin Bacon, the road to a starring role in Clint Eastwood''s Mystic River started with The River Wild and ran through France.

During that shoot, which took place just after co-star Meryl Streep finished Eastwood''s Bridges of Madison County, "Meryl told me, ''You''ve really got to work with Eastwood,''" recalls Bacon. "''I think you''d really like him. Your sensibility is the same.''"

In the intervening decade, Eastwood optioned Dennis Lehane''s Mystic River. Bacon, who heard of the option but hadn''t yet met the director, seized his opportunity in France.

"I was at the Deauville Film Festival, where Hollow Man was opening around the same day as [Eastwood''s] Space Cowboys." As soon as the lights went down on Bacon''s premiere, the actor waved at the crowd, got into a car, "then drove like crazy through winding turns, with a car full of paparazzi chasing me," he recalls. Bacon was making his way to a dinner in the countryside where he knew Eastwood would be a guest.

The actor remembers the evening with some triumph. "I go in, say, ''How ya doing, always wanted to meet you, always wanted to work with you,'' get back in the car, and walk back into my screening just as the lights are coming up."

Bacon''s efforts paid off. He had appeared in more than 45 movies in 25 years, starting with a small role in Animal House at the tender age of 19. He''s produced and directed and won awards. But-more than anything-he wanted to work with Eastwood.

Photo: Best Friends: Jimmy (Sean Penn, left) and Sean (Kevin Bacon) are haunted by childhood memories in Mystic River.

Eastwood tapped him to play detective Sean Devine, one of the three key characters of Mystic River. It''s a rare movie in which Bacon doesn''t have to write a backstory for his role; Lehane''s richly detailed book fills in the blanks. The irony, of course, is that in a movie with three stars and a complicated plot, there isn''t room for a lot of backstory. So Bacon crafts his character''s intensity and loneliness with elegance and subtlety-well suited to Eastwood''s trademark understatement.

Now the actor can talk firsthand about the Eastwood mystique. "He doesn''t spend a lot of time trying to massage your performance," says Bacon, talking in Plymouth, Mass. after a sound check for his band, the Bacon Brothers, who were scheduled to play that night at a local concert hall. "He expects you to come ready to go. He doesn''t do more than three takes."

The cast of Mystic River contains a disproportionate number of actor-directors, i.e. all three of the male leads. But Eastwood firmly denies any toe-stepping, an assessment with which co-star Sean Penn agrees. "It''s the actors who haven''t directed and want to direct that are the problem," Penn jokes.

To prepare, the cast used a few free evenings for script readings, without Eastwood. The change of pace suited Bacon. "That''s really the way I like to work. I like to do my research, figure out who the guy is, what he''s going to look like and sound like, what kind of hair he''s going to have," he says, running his hands through his own thick, well-mussed hair.

One of the biggest delights of the movie is the rapport Bacon has with Laurence Fishburne, who plays Bacon''s crime-solving partner Whitey Powers. "My character''s very withdrawn," says Bacon. "He''s not a talky-feely kind of guy. He''s holding a lot inside, and it''s eating him inside and out. His marriage is crumbling. He sneaks cigarettes. He''s become an island." Fishburne''s character, in contrast, possesses an unrelenting, in-your-face curiosity about everything around him.

The officers'' methodical reconstructions of the murder are cut with playful, almost flirtatious banter. "We wanted it to be like a marriage, and Fish had a really good instinct to try to bring a little humor into his role," said Bacon. Yet his serious, introspective detective ends up having some of the movie''s truest instincts.

The 39-day shoot took place in Boston. Eastwood was so adamant about the authenticity of the location that he commissioned the Boston Symphony Orchestra and the Tanglewood Festival Chorus to record the score he helped compose.

There''s no denying the importance of the city in a film with breathtaking shots of the majestic river, of neighborhoods that resonate with blue-collar candor, of vibrant sequences featuring a parade, a church communion, the discovery of the victim''s body in a park. Where Eastwood couldn''t find what he wanted, Oscar-winning production designer Henry Bumstead fabricated sets such as the isolated Black Emerald Bar, shot dockside.

Says Bacon, "I can''t remember the last time I had so much fun making a movie-Diner [1982], maybe. We went out every night. Clint likes jazz. Fish and I found a tiny blues bar on Commonwealth that I loved. We wrapped a week early and were all bummed out. We didn''t want it to end."