After a seven-month investigation that produced pounds of paper work and brought out a platoon of federal gumshoes, D.C. police have finally, officially decided that a suspicious wire found at the Republican National Committee headquarters here last June was not an election-year eavesdropping device but an innocent remnant of an interoffice bell system.

Assistant Police Chief William R. Dixon, relieved to close the files on this one, said the investigation was unusually thorough because of the politically charged atmosphere of the GOP headquarters then and the initial intense interest of the media. "All those forces came to bear on the situation," he said.

"The police department ended up working hard to prove that a crime hadn't occurred," Dixon said yesterday. "Normally, we do [work hard] to prove one has."

Dixon said police turned over to the U.S. attorney's office here a mountain of investigative documents, including an eight-page summary, 14 pieces of documentary evidence, 24 separate interview transcripts, photographs, FBI lab-test results and several other interim memos and reports.

The police gave the U.S. attorney "all the evidence we had got uncovered," Dixon joked.

Asked how much the investigation cost, Dixon said that, in this era of budget cutting, he'd rather not say.

Last June, the Republican National Committee cochairwoman Mary Crisp, who later left the committee in a political dispute, heard some clicking noises on her home telephone and thought it might be bugged.

A private investigator she hired said "maybe" and then checked her office at 310 1st. St. SE and found a mystery wire protruding from a wall. D.C. police stepped into the case, and the media, sensing fresh, election-year political intrigue, pounced on the story.

During the next few weeks there were confusing reports of a suspicious-looking man peering from the House office building across the street, wires running through the headquarters' ceiling and private detectives conducting electronic sweeps of offices that registered what later were to be called routine electromagnetic fields found in every office.

The FBI examined the principal suspect wire, reporting that it was a skinny strand of wire not intended for voice transmissions and one that could be purchased anywhere. Initial reports from police said the wire was connected to a Muzak system, but a Muzak official, asked by the media to look at it, later said it wasn't. The wire that aroused suspicion was dust-covered, indicating it had not been touched in years. Noise heard through the wire was inducted from contact with building water pipes, the police report said.

The National Security Agency advised police on sophisticated eavesdropping equipment. Two searches were made of the GOP headquarters and the House office building. Nothing was found.

"It just blossomed," Dixon said. "Everybody got carried away and started remembering suspicious people and then the media saw it like a second Watergate and then we had to spend all this time proving, in effect, that there wasn't a crime."