Working out of the third floor of a Silver Spring church, Margaret Rockwell has seen her 8-year-old radio station grow from a 25-volunteer force with "63 whole listeners" to one with 160 unpaid workers and an audience of 2,000--and she isn't about to give it up now.

It's called the Washington Ear and it may well have the smallest listener share in the Washington market. But Rockwell's station provides a service unlike any other: the reading of newspapers, current magazines, grocery store ads and even "Doonesbury" ("without giving away the punchline too soon") to the area's blind and handicapped.

But now, Rockwell's operation is threatened by a proposed change in Federal Communications Commission law that would allow her station to be rented to commercial interests. Rockwell and the 100 stations like hers that would be affected by the change operate on stations known as side bands. Each FM station has a side band, a companion frequency, which it controls. Under existing law, nonprofit stations may not use their side bands for commercial purposes. Instead, they use them for such public services as the reading program for the blind, adult education and foreign language instruction. It is estimated that more than 100,000 listeners across the country tune in the side bands, using special receivers.

Facing severe federal cutbacks, National Public Radio, a nonprofit network of 265 member stations--including WETA-FM, parent station of Washington Ear--recently filed a petition with the FCC that would allow it to rent its 67 kilohertz subcarrier station to commercial customers for data transmission and public utilities monitoring.

If nonprofit parent stations were permitted to rent their side channels, they could earn an estimated $60,000 a year. The Washington Ear currently pays WETA-FM $3,000 a year in operating costs, said Rockwell, but it wouldn't be able to compete with businesses for the frequency.

Yesterday, Rockwell joined a line-up of other reading-service broadcasters at a press conference to outline their strategy for keeping the Ear and stations like it on the air.

"We can understand the funding concerns of NPR," said Rockwell. "And the FCC is only trying to help them out. But somehow, we're getting caught in the switches."

Rockwell and other supporters of the reading services suggest that the FCC approve the creation of another side band channel which the NPR could then rent out for commercial purposes.

"We say, take that one," said Rockwell, "and make $10 billion if you can. Just leave us alone."

NPR executive vice president Tom Warnock said the network is fully aware of the option, but wants to switch the reading services to the new frequency, preferring to rent the exisiting 67 kilohertz subcarrier commercially because of its better sound quality.

"Crosstalk occasionally leaks through to the main channel on 67," said Warnock. "But the new subcarrier is further away from the main channel and would be less likely to interfere."

Rockwell objected to that, saying her listeners would then have to have their old receivers adjusted or traded for new ones.

The FCC, which rules in such matters, has never set limits on what a public broadcaster may do with its subcarrier station, other than the restriction to nonprofit usages, said Henry Baumann, deputy chief of the FCC broadcast bureau.

"Congress has encouraged noncommercial broadcasters and the commission to find new ways for funding," he said. "So now we're trying to maximize our usage of the FM spectrum on which the subcarriers are located ."

The FCC is likely to come to a decision by fall, said Baumann, and is now faced with the following alternatives:

* Allow the NPR and all other nonprofit broadcasters to rent out all their subcarrier stations--including a new frequency--to commercial customers.

* Allow nonprofit broadcasters to rent some subcarriers, but reserve one for nonprofit usage.

* Maintain the current ban on commercial usage of subcarrier stations by nonprofit broadcasters.

"I just hope the FCC won't do the unthinkable," said Rockwell. "If it goes the wrong way, then, of course, we'll take it to court."

The unyielding stance of Rockwell and the other side band broadcasters won nods of approval from the 40 or so supporters who turned out for yesterday's press conference.

With his black Labrador seeing-eye dog at his side, Michael Reese, a piano tuner, made the hour-and-a-half trek from west Springfield, Va., to show his concern for the viability of the reading service channel.

"The Ear has given me my independence back," he said, "even though someone else is reading to me. They're there. They're always there."