THE week before classes started in August 2004 at Franklin Central High School here, Steve George stopped in to prepare the school radio station for the coming year. As the faculty adviser to WRFT, he wanted to make sure his students were writing and producing public-service announcements. He had to contact a few of Franklin Central's football rivals to arrange for WRFT to broadcast away games. He was pricing replacements for a 20-year-old remote unit.

Then, on Mr. George's way to the station's studio, the principal intercepted him to pass along an unexpected piece of mail. It was a petition to the Federal Communications Commission asking that WRFT be denied its license, which was due for renewal, and that its frequency be given to an outfit called the Hoosier Public Radio Corporation.

Through his 34 years in commercial radio, the career he left to become a teacher, Mr. George had never once been on a station confronted in this way. He could not imagine why anyone would want to take over WRFT in particular, a 50-watt station with an annual budget of $4,200 and inoffensive programs like "Wakin' Up in a Flash," a talk show run by two seniors at the local Chick-fil-A restaurant.

"I thought, 'Is this fiction?' " Mr. George recalled. "Who could do this?"

He has since learned the answer. Hoosier Public Radio is largely the enterprise of one man, Martin Hensley, a former radio engineer who now describes his occupation as "serving God." And the effort by Mr. Hensley to take the F.C.C. license from WRFT, or at least force it to share broadcast time with him, offers but one example of a series of similar conflicts involving student radio stations. At least 20 high school stations, and a handful of college ones, have been fending off challenges to their licenses by Christian broadcasters in the last year.

This flurry of action, which seemed so inexplicable to Mr. George, actually has a fierce logic to it. A loophole in commission regulations makes educational stations unusually vulnerable to takeover attempts.

Moreover, their frequencies are a lucrative commodity, a bargain-basement way to get onto the air. The commission rarely auctions new frequencies on the crowded radio dial, and existing ones sell for $200,000 or so for a 50-watt operation like WRFT's to more than $10 million for a major commercial station.

"It's opportunistic," said Mark Goodman, executive director of the Student Press Law Center, an organization based in Arlington, Va., that provides legal assistance for student journalists. "People see this as a way to go after stations that are of value and of use. In the process, student voices can be lost, and the entire society loses. From teen pregnancy to school testing, we understand our world better and our teenagers better when we hear them."

In its original rules, the commission allowed competitors to file applications for existing licenses when they came up for renewal but also put the burden of proof on a challenger to prove the current licensee's unsuitability.

When that concept of "renewal expectancy" failed to contain the number of unsuccessful, time-consuming challenges, Congress acted in the mid-1990's to bar petitions to take over a license. At most, under the amended commission statute, a petitioner could ask the F.C.C. not to renew a given license. A loophole in the law, Section 73.561, left educational stations exposed. Such stations must broadcast at least five hours a day six days a week, and have a weekly total of at least 36 hours, to hold a license. The stations are permitted to shut down entirely when school is out of session for weekends and vacations.

Yet if those same stations operate for less than 12 hours a day, every day, they can be made to share their frequency "upon grant of an appropriate application" by a competitor.

Because the commission renews licenses every eight years, taking up applications sequentially from 18 geographical sections of the nation, the loophole went largely unused until the current round of evaluations began in June 2003.

Then the challenges came in a wave, especially as the commission took up stations in the Midwest. The petitions took aim especially at school stations close to or inside major cities — Chicago, Detroit, Toledo, Indianapolis. WRFT's 50-watt transmitter, for instance, can reach virtually the entire city of 781,000.

While Mr. Hensley went after five stations in Indiana and Kentucky, a company named R B Schools spread its efforts from Colorado to Michigan. Based in Keene, Tex., about 25 miles southwest of Dallas, R B Schools is led by Linda de Romanett, who also owns a Christian station in South Carolina.

Thus far, the commission has not upheld any of the challenges. Which is not to say the high schools have been left unscathed. Franklin Central has already paid more than $16,000 in fees to a Washington lawyer who specializes in F.C.C. law, Kathryn Schmeltzer. Some stations have bought service from National Public Radio and others, including WRFT, have bought and installed automation equipment so they can meet the 12-hour requirement without keeping pupils in the studio around the clock.

Seventeen of the stations that ultimately were granted renewals in 2004 and 2005, including WRFT, still face appeals by Hoosier Public Radio and R B Schools.

MR. HENSLEY, for one, sounds unlikely to go away quietly. He presents himself as the victim of an "emotional hate issue" all because "someone finally stood up and said these stations haven't served the public all these years." He specifically faults the high school stations for playing too much music and doing too little "community-oriented" programming, which he says should include Christian shows. Asked why he simply does not buy a station — one of the commercial Christian stations in the Indianapolis area was up for sale last summer — he points out that it ultimately brought $3 million.

Mr. George has prided himself on treating his students like radio professionals. They know from him to dress up when they broadcast from the Chick-fil-A. They know from him to avoid not only profane words but also scatological slang on the air. He has entrusted them to sell sponsorships to local businesses, much as NPR member stations do.

They have been rewarded with first- and second-place finishes for WRFT the last two years in the statewide student radio competition.

There is at least one lesson, though, that Mr. George surely wishes his students never had to learn.

"The radio station has been the best choice of my high school career," said Nicole Fisher, a 17-year-old senior who intends to major in broadcast journalism in college. "I can't believe someone would swoop in here and take it from us."