When State Superintendent of Schools David W. Hornbeck asked fourth-graders in Sheila Grisby's class in Charles County last week what they would change if they had his job, he was asking for trouble.

Air conditioning, bathroom carpeting, no music, all-day gym and more snow days, the children shouted back.

Hornbeck -- an old hand at fielding tough questions -- did not miss a beat.

"Air conditioning takes money," he said.

"And sometimes we have to make choices . . . . One of the frustrating things is that there is so much to learn and so little time and money."

It was his advice to students and to top education officials here on the hard realities of setting priorities in a world of limited resources, a lesson that may have practical applications for Charles County, which is seeking more state funds for school construction.

Throughout Hornbeck's one-day tour of county schools, local officials tried to show him that disjointed, rapid growth in Charles County will necessitate a new high school and two new elementary schools by 1990 in the northern section while declining enrollments in the rural south will require merging schools at renovated sites.

In the past 20 years, Charles County, which is less than an hour's drive from Washington, Baltimore or Annapolis, has received $55 million in state construction funds as it has changed from a sleepy jurisdiction of 23,000 residents to a bedroom community of about 80,000. The school district has 16,398 students.

All but four of the county's 28 schools are less than 20 years old and located in the county's northern high-growth crescent. But

Joseph Lavorgna, assistant superintendent for facilities, said that more will be needed as development continues.

Portable classrooms -- 20 at the most severely crowded Thomas Stone High -- sit at all four high schools. Planners say a birthrate rising since 1977 and more than 1,000 new housing units a year will put pressure on the middle schools as kindergarten classes of 120 or more begin to move through the system.

Planners have redrawn attendance areas in four of the past five years to cope with "elementary enrollments that are going wild," Lavorgna said.

The state this year gave the county a green light to plan for another elementary school in the northern part of the county and $65,000 for four portable classrooms to add to eight already at La Plata High to deal with crowding.

But requests to design an enlarged site for an eventual $3 million consolidation of Glasva and Wayside elementary schools, eight-room schools where enrollments have dropped to about 160 each, were denied by the state Interagency Committee for Public School Construction, which Hornbeck heads.

Hornbeck told school officials last week that it is "extraordinarily competitive to get capital money for school construction" even in jurisdictions such as Howard, upper Montgomery and Charles where there have been dramatic growth spurts in some areas and intense building pressures.

In 1971, when Maryland got into the business of funding school construction, $300 million was up for grabs.

This year, the pot has shrunk to $26 million, Hornbeck said.

"There are a number of places across the state with the same disjointed growth patterns as Charles," he said in an interview after his tour. "School construction is competing with everything from state prison projects to hospital roofs . . . . Given the limited funds we have and the more desperate needs in districts like Baltimore City, Charles County is a take-one-step-at-a-time mode."

But Hornbeck said that because the state has given planning approval for some of Charles projects, construction money will likely be forthcoming.

"It's not a legally binding commitment, but it is a moral commitment to construction, a recognition of a genuine need," he said.

Charles County school officials say their situation is pressing. "Because of where Charles is located, its low tax structure and its easy access to Washington, growth is happening now and it's happening fast," Lavorgna said. "We are seeing a large-scaled immigration, rather than a shift in existing population like Montgomery County."