When nearly 30,000 boys descend on the Fort A.P. Hill Army base near Fredericksburg next week for the Boy Scouts of America's National Jamboree, they will be cooking their own meals and sleeping in tents.

But the unforged wilderness this isn't.

They will be living in a makeshift city, temporarily the 15th largest in Virginia, that comes with its own bus system, telephone system and water lines, not to mention more than 1,300 portable toilets.

In fact, as long as a boy scout's hair is well trimmed before arriving at the jamboree, there isn't much else for him to worry about.

"We have no need here for a barbershop or a beauty parlor. We will have everything else you would expect in a city of 30,000," said Joe Banks of the Boy Scouts, who is supervising preparations at the jamboree site.

In case of sickness or injury, scouts will be taken to a 60-bed jamboree hospital provided by the Army, or to one of 24 satellite medical centers staffed by hundreds of volunteers.

Over 80 chaplains will be on hand to give daily services for more than a dozen denominations.

For shopping, scouts will have a choice of four trading posts, which will sell everything you'd find in a small department store.

For entertainment, the Beach Boys and the Oak Ridge Boys will be among the acts performing.

Boy Scout officials hope the 11th jamboree in scouting history will be the most successful on record, the ideal event to cap off the Boy Scouts' 75th anniversary, and to celebrate a renewed enthusiasm for scouting among today's youth.

About 28,000 scouts and 3,000 adult volunteers will arrive at Fort A.P. Hill on Monday, and stay through the closing cermonies on July 30. The jamboree will be open to the public free of charge beginning with the opening ceremonies on July 24. Both ceremonies start at 5:30 p.m.

Scout officials said they are counting on a successful jamboree to put behind them the negative publicity that came from their last national jamboree in 1981, also held at Fort A.P. Hill. Last year it was discovered scouts had been camping within 150 feet of soil that had been contaminated with dioxin, a highly toxic herbicide.

There have been no reported illnesses stemming from the 1981 jamboree, and scout officials said they are confident there is no danger of contamination at this year's jamboree.

The Environmental Protection Agency removed the contaminated soil last winter, and conducted tests giving the jamboree area a clean bill of health, said Boy Scout spokesman Robert Longley. As a show of good faith, Longley said, the Army is placing its communications center for the jamboree on the spot where the contamination was found.

"There was so much attention paid, this site is probably cleaner than any other place we could find in the country," said Boy Scout spokesman Barclay Bollas.

Jamboree officials have had their hands full, however, with just the routine logistics of preparing the 5,000-acre jamboree area for 32,000 participants, as well as a visitor crowd expected to be around 80,000 people on some days. The total cost of the jamboree exceeds $7 million, Banks said.

Some Boy Scout employes have been at Fort A.P. Hill for nearly a year, laying miles of pipe, and installing almost 500 phones and more than 1,000 showers, according to Banks.

The bulk of the work, however, is completed within the last several days before the scouts arrive and during the actual jamboree.

For example, almost 2,000 volunteers, most of them troop leaders and parents, will help the scouts prepare more than 1 million meals during the jamboree. Boy Scout officials said 117 tons of charcoal will be burned over the nine-day event to cook six tons of bacon, three miles of sausage and almost eight tons of steak.

The opening and closing ceremonies will be the highlights of the jamboree, with the Beach Boys performing at the opening ceremony, and the Oak Ridge Boys at the closing.

Other days will offer a range of attractions, Bollas said, including military paratroopers, crafts demonstrations, and career exploration booths, which will emphasize the environment and high-technology.

This jamboree has special significance, Boy Scout officials said, because it is the organization's 75th anniversary, and because the Boy Scout organization seems to have overcome the problems that plagued it during the 1960s and '70s.

"Until 1980 the numbers of scouts had been falling drastically," said Bollas, but in recent years participation has been booming.

Scouts will be attending the jamboree from all 50 states and almost 40 countries, according to Bollas. Although scouts pay their own way, selection to attend the jamboree is usually competitive, with individual Boy Scout troops deciding which members will represent them, Bollas said.

Two hundred and thirty scouts at the jamboree will come from Northern Virginia, according to Robert Cuccia, a spokesman for the National Capital Area Council of the Boy Scouts.

For Cuccia, who is scoutmaster of Troop 648 in Arlington and is volunteering at the jamboree, the event holds great personal meaning. Cuccia was himself a Boy Scout who made the rank of eagle while growing up in the Bronx.

"Scouting gave me an outlook on life that I never had before. I decided I would give something back to scouting in return for all it did for me . . . . The jamboree gives scouts the experience of associating with other people from all over the country, and this can really make an impression."