PHILADELPHIA -- Frank Gohr, a church-candle salesman from Pitman, N.J., spends a lot of time on the road and on the phone. So it wasn't unusual that he would call a client in Baltimore from a pay phone in a Mullica Hill, N.J., restaurant.

What was unusual was the cost of the call. Gohr was charged $2.70 for that two-minute call in October, a call that would have cost no more than $1.30 had it been handled by the long-distance firm whose credit card he carries, AT&T.

Instead, Gohr's call was intercepted by Central Corp. of Fort Lauderdale, Fla., one of a new and fast-growing category of long-distance companies that offer "alternative operator services" (AOS).

The AOS industry is attracting considerable attention from state and federal regulators who are alarmed by consumer complaints of price-gouging and fraud. But executives at the companies say that many of the complaints involve technical glitches that eventually were made good and that the regulators preparing to crack down on their business practices don't understand the industry.

"I expect to pay a premium on {operator-assisted} calls, but I don't expect to pay the usurious rates that they're charging," Gohr said of the bill he received from Central for the call to Baltimore and another he placed from the same phone to Lebanon, Pa.

Gohr complained to the Federal Communications Commission, which can do little more than present his complaint to Central. Because the AOS firms are not considered long-distance carriers by the FCC -- they merely buy and resell long-distance time from regulated carriers such as AT&T, MCI and US Sprint -- the commission has limited authority over them and the rates they charge, said Kathie Kneff of the FCC's common-carrier enforcement division in Washington.

She said the commission could fine companies that refuse to respond to consumer complaints. Most consumers who have complained to the FCC about rates have received refunds after the FCC contacted the companies, she said.

AOS companies are going after a $7 billion-a-year market for calls made by dialing zero, then the number. That includes person-to-person, credit card and collect calls, and calls billed to third parties. Many of those calls are made from coin phones and room phones in hotels, motels and hospitals.

Until recently, almost all those calls were handled by AT&T. But in 1984, AT&T stopped paying 15 percent commissions to hotels for long-distance calls by guests. That opened a market for AOS companies.

At least a half-dozen companies began approaching hotels and hospitals with an attractive offer: Let us route all zero-plus calls generated by guests or patients through our long-distance resale network, and we'll give you a cut of the revenue.

So-called zero-plus calls dialed on an AOS-controlled room phone or pay phone are routed to an operator who works for the AOS company. The operator collects billing information from the caller, then sends the call on its way over a line leased from one of the long-distance companies.

Many consumers have complained that they didn't know a call was being handled by an AOS operator until the bill arrived. The AOS firms say they tell their operators to identify the company they work for and to transfer to AT&T those callers who specifically request an AT&T operator.

A caller is billed either to a telephone credit-card company or a local phone company, which do billing for all the long-distance companies.

Entrepreneurs who invented the AOS idea say it was a stroke of genius. Hotels, motels and hospitals welcomed the offers, and the AOS companies took off.

Central was one of the most successful. In 1986, its startup year, revenues were $165,000. Last year, it took in $19 million. The company has 365 operators handling calls from 180,000 telephones in 47 states, according to its president, Lester Freeman.

"AOS could get so big it's mind-boggling," said analyst Edward Becker of Williams Securities in Tampa. "The potential out there is in the billions."

But regulators in several states take a dimmer view of the industry.

Public service commissions in Florida and Tennessee have proposed regulations to limit AOS rates. The Virginia Corporations Commission has issued a "consumer alert" regarding the companies.

When making a call from "a hotel, motel, hospital, airport, college, or pay phone that uses alternate operator service" you don't normally deal with, "you are dialing at your own risk," the alert said.

In New Jersey, a staff report that will recommend regulatory action on the companies is being prepared for the Board of Public Utilities, according to spokesman George Dawson. The Pennsylvania Public Utility Commission has proposed rules to govern rates charged for pay-phone use but has not taken steps to regulate charges for using room phones, said Joe Farley, manager of the PUC's telecommunications unit in Harrisburg.

If approved after a hearing expected in August or September, the proposal by the Florida Public Service Commission would require all AOS firms to be regulated as "interconnect" companies, thus putting them under the same regulations as other long-distance companies. Under the Florida proposal, AOS firms would not be allowed to charge end-users rates higher than AT&T's.

In Tennessee, a Public Service Commission proposal would prohibit local telephone companies from providing billing services for AOS firms that charge more than AT&T.

In a report to the Florida Public Service Commission earlier this month, Adam Taylor, chief of service evaluation, said the firms should be more stringently regulated because there are no market pressures to keep rates low.

"When AOS representatives talk about their customers, the commission should keep in mind that they don't consider the end users to be their customers, even though that's who gets this bill," Taylor told the commission. "Customers to an AOS are hotels, motels, universities, hospitals and pay-phone providers who share in the profits for calls diverted from the end user's preferred carrier.

"This sharing of profits has doubtless contributed to the rate-gouging that has occurred. The higher the rates charged, the more revenue there is to share. Thus the end user becomes the end loser."

AOS executives such as Freeman scoff at such criticism and say customers apply pressure to keep rates low. "The hotel manager and hotel owner is critically concerned about the quality of service and the cost of service to his guests," Freeman said.

Harvey Stanley, president of Elcotel Inc., an AOS company based in Sarasota, Fla., said hotel guests should expect to pay a premium for zero-plus calls from a hotel room. "If you want to drink a beer, the cheapest place to do it is at home. If you go to the hotel bar, you're going to pay $2.50,'' he said.

All of the AOS firms combined probably hold less than 1 percent of the zero-plus market, he added.

''But at some point,'' he said, ''AT&T is going to notice that they're there. And when that happens we may see {AT&T} push the FCC to start regulating {AOS} interstate calls.''