Watch out Ronnie Reagan, Joe Adamov is out there waiting to steal your thunder.

Sometime next week, if all goes well, radio fans around Sterling, Ill., will be the first to hear the man Radio Moscow is touting as "Moscow's answer to Ann Landers" when station WSDR -- better known as "The Voice of the Rock River Valley" -- introduces Adamov and his ever-popular program, "Moscow Mailbag."

The station is one of about 400 in the U.S. on the Radio Moscow mailing list. But only a handful use the material, according to federal officials, and most of those are small college stations that take the Soviet syndicate's music or language offerings.

Listeneras to the little 500-watt radio station, located 100 miles west of Chicago, will get a weekly sampling of English-language Moscow restaurant reviews, broadsides against rising cab rates in the Soviet capital and a few shots at the way the U.S. press handles stories about Soviet dissidents.

"We plan to run the show right after our Ronald Reagan commentary," said Carey Davis, the 24-year-old station manager and morning news anchor at WSDR.

That is, however, unless the Justice Department speaks up first.

When WSDR accepted a Radio Moscow offer last month to supply a weekly package of programs, it ran into one of those regulatory tangles that Washington knows so well.

Under the government's 1938 Foreign Agents Registration Act, WSDR may have to register as a Soviet agent here if it runs the Radio Moscow material. But under the 1934 Federal Communications Act, a foreign agent is not allowed to hold a U.S. radio license.

"We are not going to put a thing they've sent us on the air until we get a ruling from the Justice Department," said Davis, whose family also owns the Sterling radio station.

The Justice Department's foreign registration section -- the same unit that recently was asked to determine if Billy Carter was a foreign agent for Libya -- is looking into the situation.

Joel Lisker, the Justice Department attorney here who is handling the case, siad yesterday that the 1938 statute on foreign agents is aimed mainly at persons who are paid by a foreign government to influence opinion.

"If the Soviets paid them to do what the radio station wants to do then they would have a problem," said Lisker. Since the Radio Moscow programs are free and the Soviets are not lining up sponsors for them, it is unlikely tat WSDR will have to is unlikely tat WSDR will have to keep the shows off the air, he said.

Nevertheless, the Justice Department is not likely to make its formal ruling in the case until next week Lisker said.

"We want to see if there might be any overriding international ramifications to this," he said, adding that the Justice Department is checking with officials at the State Department and the International Communications Agency.

Maanwhile, back in Sterling, they are making big plans to introduce the Radio Moscow programs with a flourish. "We're going to start putting them on and throw open our microphones for anyone who wants to call in," Davis said. "A lot of our listeners are farmers and you'd be surprised how many of them have been to Russia." the Voice of America, Davis said. "They want to translate the shows into Russian and beam them back at Moscow," he said.

It is only fitting, said Davis, that his radio station be the first to introduce the Soviet commentators since it was the first in the United States to run Reagan's syndicated show two years ago.

A spokesman for the Los Angeles Since announcing its intention to broadcast the Radio Moscow shows, the Sterling station has heard from firm which now syndicates Reagan to nearly 300 radio stations said yesterday company officials had not heard of Joe Adamov and they were not worried about competition from the Moscow Mailbag.

"We compete with plenty of other syndicated columnists," said the spokesman. "We consider this just another part of the free enterprise system."