After Nancy Lappert went back to work three years ago, she and her husband Randy thought the pool in their Columbia, Md. neighborhood would be sufficient summertime amusement for their two young daughters, who are looked after by a baby-sitter during the day. But their daughters were "bored as can be" after a while, Randy Lappert said.

This summer when the family assembles for dinner, the girls, aged 7 and 10, are "exhausted" and full of talk about their days filled with horseback riding, swimming, tennis, and arts and nature activities at the Circle D Farm Summer Day Camp near Olney, Lappert said.

"You don't leave children home all day -- they'll get into trouble," said Silver Spring physician Charles L. Franklin, whose two daughters also attend a day camp. While he trusts his children, Franklin said, "an idle mind is the devil's workshop."

Franklin, who is divorced, has custody of his daughters during the summer. They have attended Barrie Day Camp in Silver Spring since 1979.

Idle childhood summers are becoming an archaic notion in neighborhoods of Prince George's and Montgomery counties, where school and recreation department officials say there is a strong demand not only for summer custodial programs, but fulfilling activities for children.

"People have gotten very sophisticated. You just don't send your kids out the door anymore," said Darald Lofgren, chief of the Montgomery County Recreation Department's programs division. Lofgren also suggests that parents' fears about the safety of their children could be helping fuel the "tremendous increase" in organized activities for children.

Lappert said that at camp, his daughters "are being exposed to new things I'm not capable of giving them on a daily basis."

"I would probably put them in camp even if I wasn't working because we don't have a lot of children in our neighborhood," said Catherine Mooney, whose son and daughter also attend Circle D. "It's more to give them something fun to do."

"I know I could have gotten a baby-sitter but I'm sure he would have spent most of the day watching TV, and I don't want him doing that," said Donna Braxton, a nurse who sends her 9-year-old son to the Barrie camp.

"Some people take the attitude that you are throwing your children away to get them out of the way," Lappert said. "I don't look at it that way. I don't force them to go. They love it."

"I get a whole new set of friends there and it's a lot better than staying home, " says 12-year-old Rasheed Salahuddin of Fort Washington, who goes to Camp Meadowbrook in Suitland.

"I get to look out for the little kids and watch them by the pool and stuff," said Rasheed, who is a counselor-in-training.

Private day camps serving the Washington area and camps and programs offered by Montgomery and Prince George's schools and recreation departments are as popular as ever, despite a decline in the number of school-age children in both counties, county officials said. And the growing number of working mothers and single parents is a significant factor in their popularity, they said.

Circle D camp director Tim Dowd said he had to expand his hours of operation to accommodate working parents, whose children make up 70 percent of his enrollment.

Montgomery County summer school programs have enrolled about 17,000 students for each of the past five school years, despite a decline in regular school year enrollment during that period, said Cornell T. Lewis, summer programs director.

In addition to basic academic courses, schools in Montgomery or Prince George's offer a variety of special and enrichment courses for all grades in the arts, sciences, computers, music and languages. The courses are in demand and students have to sign up early, school officials said. Fees, which are charged for most courses, range from $36 to $72 in Montgomery and from $25 to $158 in Prince George's. Montgomery offers French and Spanish language camps and an outdoor "ecological adventures" course that includes a crabbing trip to the Chesapeake Bay. There are also courses in vocational skills and for the gifted and talented as well as special education classes for students with learning problems.

Susan Lewis, 14, an A student in her Spanish classes at Herbert Hoover Junior High School in Potomac, is going to Montgomery County schools' Spanish camp this summer because "I'm really interested in the Spanish culture and it was always my favorite subject."

Michael Ware, 13, of Washington, said that if he wasn't attending camp this summer, he probably would have just stayed home and rode his bike, something "I would not have rather done." At Camp Meadowbrook, Ware said, "we get to do a lot of fun things, like long nature hikes, swim a lot and play softball."

In Prince George's, older students "are dying to get into" the 15-day Reserve Officers' Training Corps (ROTC) program, said the county's summer education supervisor Eleanor C. Rotter. Students in the program live at the Fort Meade Army base and tour the Pentagon and Andrews Air Force Base in Camp Springs.

Rotter said about 30 percent of the county's summer students are taking courses for extra credits and enrichment.

The county's recreation programs are also growing in popularity, said Steve Davis, spokesman for the Maryland-National Capital Park and Planning Commission, which directs the programs.

Organized or drop-in programs and classes for preschoolers to adults are held at schools and community centers throughout the county, Davis said. Two-week recreational, sports or specialty day camps are also available and in demand.

"People have to act quickly" for Montgomery summer recreation programs that "fill up fast," Lofgren said. The 31 day camps operated by the county "would have very few openings at this time," he said.

In contrast to the steady popularity of local day programs, the long-established residential camps located primarily in mountain and rural areas are said to be experiencing a slump in demand.

"Enrollment is definitely on a decline" for the 42 area residential camps represented by the American Camping Association, said Brother Tom Vadden, spokesman for ACA's Chesapeake section, which covers Maryland, Northern Virginia and parts of West Virginia.

Such camps' higher fees are keeping some people away, and some children "don't want to be away from the boob tube for eight weeks," said Elizabeth Sibbett, who runs the Camp Advisory Service, a camp consulting service in Monrovia, Md.

Parents "gasp" at the fees, which can range from $1,600 to $3,200 for eight weeks of camp, Sibbett said. The fees go in part to cover the growing costs of operating residential camps, including liability insurance for the horseback riding and swimming activities, salaries for qualified instructors and counselors and food expenses, she said.

Private local day camps cost about $85 to $93 a week, Sibbett said, with additional charges for transportation and extended day-care services. Camps run by scouting groups, churches and the YMCA cost considerably less, she said.