In order for actor Martin Sheen to direct his first feature-length movie, he needed to land his son Charlie for the starring role.

His motives were twofold. In his son, the elder Sheen saw a very talented actor for the lead, and one who could be pursuaded to take the job at a fraction of his usual six-figure salary.Filial piety and family loyalty won out, and Charlie Sheen took the role in "Cadence," a '60s drama of race relations and conflict in an Army stockade in West Germany during the Vietnam War.

In addition to directing Charlie and himself (as a bigoted stockage sergeant), Sheen also directed son Ramon Estevez in a supporting role in the low-budget movie.

While noshing a pizza the other day in a Malibu restaurant half-owned by Charlie, papa Sheen reflected on his good fortune in being able to work with his sons.

"There's no way `Cadence' would have been made if Charlie hadn't agreed to do it for nothing," his father said. "Nobody was going out of their way to ask me to take a directing job.

"The budget on the film was too small to find a distributor, but New Line Cinema thought if Charlie played the lead they could at least get back their investment. Charlie agreed with the proviso that I would be the director.

"Personally, I think it is the best work he's ever done. I had acted with Charlie in `Wall Street' and we discussed a few things during the production. But it was altogether different directing him and Ramon.

"It was very special directing my sons, almost sacramental - and I don't say that lightly. It gave me an opportunity to experience them in ways only I knew were available to us.

Sheen offers unbridled praise for Charlie and Ramon.

"To have them as sons is a blessing and to have them as friends is a blessing and to have them as fellow actors is an additional blessing.

"I was permitted to go into places in their hearts that no other director would know existed. That's why I think Charlie's performance was so good. He exposed himself thoroughly. That was very gratifying.

"I asked for permission to take them to places only I knew, as a father, were there. I promised in return I would not ask them to try anything I wouldn't do or take them anywhere I would not go. They trusted me.

Sheen says the father-son relationship that was the foundation of their rapport occasionally was a barrier.

"Sometimes it got a little touchy and I told them to forget that I was the old man and to try a scene another way because they wouldn't like themselves - or me - if they settled for less than their best. I couldn't talk that way to other actors.

"There were times when the boys were reluctant. Charlie has a good natural instinct that is second nature to him because he's been around sets since he was a little boy."

While his sons turn in outstanding performances, Sheen can take equal pride in capturing some of the most remarkable footage ever of the world of blacks in the absence of whites.

"The thing I worried about most on this picture was being white," Sheen said. "I didn't want to impose my background, my whiteness, on their community. I didn't want to see their relationships through white eyes.

"The only thing I can take credit for is bringing them together, offering my friendship and my desire to become a conduit for the black community. They agreed and were very helpful and compassionate.

"From the beginning I asked Larry Fishburne, Blu Mankuma, Michael Beach, Harry Stewart and John Toles-Bey (the five superb black actors) to improvise as much dialogue as they felt comfortable with, telling them I would get out of the way.

"I said, `I know what's written in the script, but how would a real situation like this develop if there were no whites around.' They understood and as a result some scenes are fantastically enriched by their ad libs and body language.

"They came through with everything I hoped they would. All of the credit for the spontaneity of their performances belongs to them."

Now that Sheen has made his debut as a feature film director - he previously directed the TV movie "Babies Having Babies" co-starring daughter Renee - he is anxious to put together a film project starring his three sons, Charlie, Ramon and Emilio Estevez and daughter Renee.

"I'm trying to do a movie about Pop Warner, the great football coach, with Emilio as Warner and maybe Charlie as Jim Thorpe," Sheen said. "My family is very talented and working with all of them in one picture would be a wonderful experience for me."