For the Cliffs of Oxon Hill and the Selwoods of Bethesda, soccer is a family affair. Gene and Nancy Cliff are both soccer coaches and each of their nine children plays. Peter Selwood coaches, his wife Beverly is administrator of the club and their three children belong to teams.

Like hundreds of Washington area parents, the Cliffs and the Selwoods boost soccer with the same fervor most parents put into telling their kids to eat their carrots. In the metropolitan area, an estimated 75,000 youngsters under the age of 19 are registered to play the sport.

Both families were well represented last weekend when 1,700 youngsters in 114 teams from seven states and the District of Columbia competed in the Bethesda Soccer Club Tournament.

Cliff, a Navy officer stationed at the Pentagon, coaches the Oxon Hill Boys 1969 soccer team (made up of youths born in 1969). His wife Nancy, a former physical education teacher, coaches two girls teams and plays on a women's league team.

The oldest daughter, Donna, 22, who graduated from the Air Force Academy, played on the boys team at the Air Force Prep School. Diane, 21, plays with her sister in a league in Colorado Springs. Vicky, 20, plays for Salisbury State University. Steven Maisel, 20, the Cliffs' adopted son, plays in a recreation league at the University of Maryland. Richard, 19, plays on the varsity team at George Washington University. Sally, 18, plays for a team in Camp Springs. Jamie, 16, played on the varsity at Oxon Hill High School until he broke his leg earlier this season. Susan, 14, and John, 12, play for the Oxon Hill Boys and Girls Club teams.

"The toughest part about having so many kids involved in soccer is trying to keep the uniforms straight," says Gene Cliff.

Selwood's family, while smaller, is just as active. Selwood, a mortgage banker, coaches and is the former commissioner of the National Capital Soccer League, the largest league in the metropolitan area. Beverly Selwood is an organizer and administrator of the Bethesda Soccer Club. Chris, 13, plays on the team Selwood coaches in the Bethesda league. Michael, 12, also plays in that league and Amy, 8, plays in the Washington Area Girls League.

As he handed out trophies to the winning team in the 1968 Division at the Bethesda tournament last weekend, Selwood ticked off the reasons he sees for soccer's popularity. "For one thing," he said, "it is a low-cost sport. It's also a team sport that anyone can play. There are a lot of teams that have handicapped children on them. Also, there is a universal appeal about the sport. The youngsters get to travel and meet lots of other children and they don't even have to speak the same language."

Selwood's interest in the sport has mirrored soccer's growth in Maryland. In 1972, when he first got involved, 250 kids played soccer in Montgomery. "Now, there are close to 15,000 children playing in the county," he said.

Because soccer leagues are divided into two types of teams, advanced and open, Selwood said, there is not as much competitive pressure on players as there is in football, baseball or basketball.

"This isn't a sport that kids can go to a local park and play, like basketball. Soccer takes a commitment from the child but also one from the parents," he said. Selwood said soccer parents more often "are realists when it comes to seeing what their children's abilities are" than are parents of other young athletes.

"The support given the children is extremely important. But it's more than making sure that the child is where he or she is supposed to be," he says. For Selwood on tournament Sunday, support meant helping his boys, Chris and Mike, work their morning paper route at 5 a.m. and then going with them to the tournament field. With seven other fathers, he readied the field by removing the football lines and laying down lines for the first soccer game at 9 a.m.

"As a coach, I sometimes have to tread a difficult, thin line in dealing with parents, who have trouble assessing their role in the child's soccer development," Selwood says. "We try and keep the parents somewhat removed from the game. But really the game itself provides a shield by being somewhat unstructured. Once the ball is in play, there's not much a parent, or for that matter, a coach, can do. In other sports, the parents yelling at the kids can be heard clearly, like when the child is in the batter's box or at the foul line. But that's not the case in soccer."

Guy Fraiture, who coaches at Georgetown Prep high school and is a referee for the North American Soccer League, has two sons, Christian, 13, and Sacha, 9, who competed in the Bethesda tournament. He said, "If you say to a youngster, 'Go into a playground and play,' he's not restricted and there is an unbridled enthusiasm. As the child gets older, in most sports, restrictions come into play, like weight and size. But in soccer, a small boy can face a bigger one.

"I have a son who likes to play football. But I'm reluctant to let him play," Fraiture continued. "Soccer is a contact sport, but the type of contact in football is to the vital parts of the body."

For the Cliff family, soccer has become a way of life. Dinner conversation more often than not centers on the sport.

"But," Nancy Cliff cautioned, "we're naturally a sports-minded family, so it's been no major adjustment. The toughest part is getting all the paperwork and the fees sorted out. I'm not a paper person."

She says that with so many people playing, "sometimes we've exchanged cleats either by accident or by necessity. One time I almost cut off the circulation on my toes. One of the boys once was forced to wear his sister's cleats. That was pretty embarrassing for him." Now they've solved that problem with different-colored shoelaces.

With nine children and two parents, the Cliffs can field a full team. "We used to play together and challenged one of the boys teams to games," Nancy Cliff recalled. The Cliff family team was "hard to beat," she added.

Here are the results of the Bethesda tournament:

BOYS

1967: Little River, Va. 3, Gladwyn, Pa. 1;

1968: Vienna, Va. 2, Reston 0;

1969: Rockville 1, Oxon Hill 0;

1970: New Castle, Del. 2, Little Flower, Baltimore 1;

1971: Montgomery 2, Bethesda 0;

1972: Kettering/Largo 3, Bayonne, N.J. 0;

1973: Bethesda 5, Prince Williams, Va. 0.

GIRLS

1968: Bethesda 3, Wheaton 1;

1969: Montgomery Soccer Inc. 2, Annandale, Va. 0;

1970: Bethesda/Montgomery 2, McLean, Va. 0;

1971: Bowie 3, Arlington 1.