When youngsters showed up at the Somerset-Olde Creek community pool near Fairfax City yesterday, they got a firsthand look at how soaring insurance rates will affect their summer fun: The pool's high diving board was gone.

Rising insurance costs, which have caused cities, day care centers, midwives and other so-called high-risk clients to lose their insurance coverage or pay 10 times their old rates, are taking the spring out of summertime diving across the Washington area.

At least 100 community and private pools have had to remove their high diving boards because insurance companies told them the boards go, or their coverage goes.

Insurance companies and underwriters say they are fleeing high-risk fields because they threaten to make them bankrupt. Accidents that occur on high diving boards, they say, too often do not mean bruised big toes, but costly, lifelong injuries.

"It's in the same high-risk category as an explosive manufacturing firm," said William E. Cox, president of Cox Insurance Associates in Arlington. "You don't get a little bit hurt."

Bruce O'Hara, the manager of the Somerset-Olde Creek Recreation Club, said he has seen the pool's annual insurance bill jump from $350 to $6,500 in five years. To trim $2,500 off that latest figure, O'Hara summoned a maintenance firm last Sunday to take down the three-meter diving board.

"We're up a well-known estuary without a means of locomotion," said O'Hara as he and hundreds of others in the area prepared for pool openings this Memorial Day weekend. "If this gets any worse, I'm going to be out of the pool business."

Another Fairfax club, the Mantua Swim and Tennis Club, has seen its insurance leap from $4,000 last year to $12,000, in part because it decided to keep its high board.

For many of the 16,000 members of the Northern Virginia Swimming League, the largest community summer league in the country, and the Montgomery County League, the lack of high diving boards means they will have difficulty securing as much practice as most would like for their diving teams.

"It hurts the diving program," said Nancy Methfessel, 18, a former all-star diver from Robinson High School in Fairfax. "If you want to go above the summer league level, you have to do three-meter dives."

Such practice, she said, "is very, very important for getting college scholarships and getting into all-national meets."

Some small pools may have to close because of the rising insurance costs they face, O'Hara said. It's particularly upsetting because swimming and diving are among "the few sports left in the Olympics that we dominate."

Stefan Nickodem, the president of Clearwater Inc., a pool management firm in the Washington area that has removed several diving boards this year, estimated that 50 percent of the "hundreds of pools that have had high dives" in the Washington area are cutting them down.

Many swim coaches say they are surprised that 1986 is the year diving suddenly has become a big risk.

"In competitive diving, an accident is very few and far between," said Dr. Joseph Fratantoni, a member of the Montgomery Country Swimming League board of directors.

He said a few lawsuits resulting in million-dollar awards have panicked insurance companies and caused the premium increases or total refusal to insure.

A 10-year California study completed in the late 1970s found that 2.5 percent of accidents that resulted in paralysis occurred in pools, and the vast majority of those happened in apartment, hotel and other noncompetitive pools, said Fratantoni, a laboratory chief at the National Institutes of Health.

It would be a shame for "something as good and healthy as swimming" to be ruined by irrational increases in insurance rates, he said. Jay Angoff, counsel to the National Insurance Consumers Organization, agreed that the number of accidents has not increased and said jury awards hardly justify the tremendous rate increases.

Swimming, however, is not the only youth activity affected. The Boy Scouts of America's national headquarters disclosed last week that its annual insurance premiums have jumped from $2 million in 1984 to $10 million, a boost large enough to force the organization to talk about increased dues