The small understated black-and-white law shingle in front of the comfortable town house at 6 W. 3rd Street blends unobtrusively with the street in this quiet and stable town of 28,000 residents 45 miles northwest of Washington.

But inside 6 W. 3rd Street, things are not so quiet and stable these days. One of the two partners in the law firm--Richard Mark Winters, 33, a successful criminal trial lawyer, has been indicted by a federal grand jury investigating a cocaine conspiracy. The other partner has troubles too--he and Winters have been indicted by a state grand jury on charges of tax fraud concerning income from their law practice.

Seven other Frederick area persons indicted in the cocaine investigation constitute a cross section of professionals--a building contractor, a former banker, a real estate salesman--plus a pair of country-and-variety musicians.

In a series of three indictments and one criminal information returned last month in Baltimore, federal prosecutors alleged a high-stakes cocaine conspiracy in which several suspects conspired to import the drug from Bogota, Colombia, by commercial airline to the Frederick area from the summer of 1978 to the fall of 1980.

Other members of the group allegedly conspired to sell and distribute quantities of the drug, ranging from a few grams to several pounds at a time, in Frederick County, adjacent Carroll County and possibly the eastern panhandle of West Virginia, according to prosecutors. Local police estimated the cocaine's wholesale value at $45,000 to $60,000 a pound.

Parts of the operation, they alleged, were financed by phony bank loans authorized by a Maryland National Bank branch manager in Frederick, who in an unrelated case was convicted in 1981 of embezzling more than $180,000 from bank customers.

At the state level, a grand jury in Annapolis returned an indictment last month against Winters and his partner, Robert D. Osburn, 38, an aggressive real estate lawyer and entrepreneur, charging them with under reporting their law firm income on tax returns during the same general period covered in the federal indictment. Investigators would not specify how much income the two allegedly failed to report. The nine-count indictment said they reported incomes ranging from $44,898 to as little as $5,773 each per year.

Only Winters is charged in the federal cocaine conspiracy indictment, and Maryland Assistant Attorney General Gary P. Jordan, chief of investigations, stressed in an interview that while his office conducted a joint investigation with federal authorities, the state tax indictment against the two men involved only business income from their law practice and not any alleged sale of cocaine.

Winters and several other defendants were arraigned in federal court in Baltimore on Friday and pleaded not guilty to the cocaine charges. Other defendants will be arraigned later and are also expected to plead not guilty.

Osburn and Winters are scheduled to be arraigned on the state tax charges in Annapolis next week. Both lawyers declined to talk to reporters.

Police officials, real estate dealers and other attorneys in Frederick described the two men as successful professionals.

"They are substantial members of the legal community in Frederick," said a state investigator who asked not to be identified.

Winters, who is originally from nearby Brunswick and maintains law offices there as well as in Frederick, has developed a busy criminal law practice, representing scores of defendants, mostly for petty offenses, in the circuit and district courts of Frederick County, according to fellow lawyers.

Osburn is known more as a real estate attorney and businessman, and is part owner of several commercial properties, including the rural Catoctin Mountain Inn restaurant near Thurmont, just north of Frederick, according to mid-1982 county tax records.

Osburn and his wife, Gail, own a large home and adjacent land on Baughmans Lane in Fredrick assessed at $170,580, according to the tax records. Winters owns a somewhat smaller house next door assessed at $52,450, according to the records.

The joint state-federal investigation leading to the indictments began in the summer of 1980, headed by Maryland Assistant Attorneys General Jordan and Bruce C. Spizler, Special Agent William L. Athas of the U.S. Drug Enforcement Agency and Assistant U.S. Attorney David B. Irwin. Their examination involved loan records in the Maryland National Bank embezzlement case in 1981 and touched on at least two witnesses involved peripherally in a marijuana-related murder trial here recently.

Larry Paul Weddle, 38, a 13-year branch manager for Maryland National Bank in Frederick, was convicted in 1981 of embezzling more than $180,000 from the bank and from a local Moose lodge where he had been secretary for several years. Winters represented Weddle at trial.

At the sentencing, Weddle testified that he was a compulsive gambler--especially sports betting-- and the judge suspended all but three years of a 10-year sentence and ordered him to serve it in a halfway house.

Within weeks, however, cocaine was discovered in his body during routine urinalysis, according to investigators, and he was transferred to the Maryland House of Correction in Jessup.

Thereafter, investigators said, they looked into whether Weddle may have spent some of the embezzled money on "drug activity" rather than gambling. State investigators began swapping information with DEA agents and looking into the tax returns of specific acquaintances of Weddle.

Last September, DEA agents and state police with search warrants raided the home of Steven Richards Smith, 30, a Frederick real estate salesman and a friend of Winters, seizing what they said was a pound of cocaine. Next, they said they raided Winters' law office and home, seizing small amounts of cocaine and marijuana and what they described as "documentary evidence."

By last week, eight persons had been charged in the federal conspiracy cases, and Winters and Osburn had also been charged with state income tax fraud.

Weddle was charged in a federal information with authorizing $20,500 in two phony bank loans to unnamed co-conspirators to finance flights to Colombia to obtain cocaine.

Winters and Smith were indicted on charges of conspiracy to possess and distribute cocaine. In a separate indictment, James Stephen Selckman, 25, formerly of the Frederick area and now living in Anne Arundel County, was also charged with conspiracy to distribute cocaine.

Five persons were indicted on charges of conspiracy to import cocaine from South America in a series of at least six airline flights. They were identified as: John Paul Daiger, 45, a building contractor in Howard County; David Buchanan Gardiner, 26, formerly of Frederick and now a member of a country-and-variety music group called "Easy Pickin's" in Charles Town, W. Va.; Kirk Laverne Esworthy, 28, another musician, of Frederick; Bruce Thomas Joy, 30, of Frederick, and Mary Lucille Post, 23, formerly of Frederick and now living in Sunnyvale, Calif.

Gardiner and Smith entered pleas of not guilty, along with Winters, at last Friday's arraignment in federal court.

Frederick County State's Attorney Lawrence A. Dorsey Jr. said Daiger and Esworthy were minor witnesses in the Frederick County murder trial of Robert C. Kehne Jr., convicted of shooting auto salesman Michael L. Bruchey in 1978 in a drug-related case. Dorsey said Bruchey gave a 40-pound bale of marijuana to Kehne, who then killed Bruchey rather than pay him approximately $10,000 for the drugs. Daiger testified that he was among the last persons to see Kehne alive, and Esworthy said he had once possessed the pistol that was later used in the slaying. Neither Esworthy nor Daiger was implicated in the slaying.