At Orange Hunt Elementary School in Fairfax County, the din from the cafeteria is deadened somewhat by wall-to-wall carpeting outside in the hall. But once the double doors open, the racket becomes deafening. It is clear that the spacious lunchroom holds many more children than fit comfortably.

A once-open media center in the middle of the school has been closed off as a barrier against hoards of children who enter the building from temporary classrooms and trailers parked behind. The passing traffic still causes heads to look up from studies.

Orange Hunt Elementary, orginally designed for fewer than 700 pupils, now holds 1,040. The school look for relief from crowding through a special $39.7 million bond referendum Tuesday.

It will be the second school bond referendum in less than a year. Last June voters approved $19.7 million for new school construction in the fifth school bond referendum in five years. Tuesday's voting will be held 6 a.m. to 7 p.m. at regular polling places in the county.

If voters approve the bond sale, the county school board has promised there will be no referendum for another two years. At the end of that time, school officials say, more bond issues will be needed to finance new schools for hundreds of children expected to come from new development in southern Fairfax and the Reston and Great Falls areas.

This year's bond issues would pay for seven new schools in these fast-growing areas to take children from overcrowded schools like Orange Hunt in Springfield and make room for new students.

About 15 miles from Orange Hunt, at Centreville Elementary School, principal Shelton T. Belsches has no problems with lack of space. In fact, Centreville could hold 75 more pupils than it has.

But Belsches says he worries that one day some child will run into exposed radiators in part of the 40-year-old school cafeteria that is used as a gym.

He said he recently transferred a teacher to another school at her request because she was unable to work uner the poor lighting provided by 20-year-old hanging globes.

If voters support the bond sale, $9.8 million of the $39.7 million total would be set aside to imporve Centreville and seven other schools that have substandard ceilings, heating, lighting and plumbing, and lack ramps and other facilities required by law for handicapped children.

New gyms, music areas and media centers would be added or improved at four elementary schools - Centreville, Churchill Road, Woodley Hills and Kent Gardens - to make them more similar to newer ones. Additional improvements would be made at four secondary schools - Longfellow and Glasgow intermediate schools and Fort Hunt and McLean high schools - including auditoriums and rooms for music, fine arts, business education and home economics.

Air conditioning would be installed in all central offices, cafeterias, auditoriums and other parts of the building used year-round.

"The buildings aren't going to fall down or anything like that if this upgrading isn't done," said Thomas F. Hanton of the schools construction offices. "But it's a waste of time and money not to do it now when needed."

He said the schools' proposed $264 million operating budget for next year would have to pay for safety-related repairs if the bonds are not approved.

The $29.6 million of bond money earmarked for new construction would pay for building three elementary schools and one intermediate school in the northern part of the county - Mumford Park, Great Falls No. 2 and Herndon/North Reston elementaries, School also serving Reston. It would also pay for building two elementary schools and another intermediate school in the fast-growing southwest section of Fairfax - Rolling Valley West and Burke Center elementaries and Chantilly Intermediate.

School planner Donald Schudel said most of the schools would be filled to capacity when they open. Most would open in school year 1979-80.

The design for most of the elementary schools calls for three bay areas containing classes divided by portable partitions radiating from a central core that contains a library, cafeteria, offices and gym.

About $293,000 of the bond money would renovate an elementary school to provide a center for the emotionally disturbed in the northern part of the county. The school to house the center - called the North County Center for the Emotionally Disturbed - will not be identified at least until next year, after results of an extensive report on declining school enrollment in the older, eastern sections of Fairfax is studied by the school board to develop a procedure for closing schools.

County Board of Supervisors member Warren I. Cikins was the only one to abstain in otherwise unanimous support for the bond referendum from the supervisors. He said he felt the results of the school enrollment report, which would indicate what schools might close, should be available before holding the referendum, but added that he now supports the bond issue.