Carl L. (Cobby) Lynch, who ran an East Coast drug ring that used scores of fat women to obtain prescriptions for amphetamines that were then sold on the street to drug users, was convicted here yesterday of racketeering, conspiracy, illegal distribution of drugs and interstate travel for racketeering.

Eight other co-defendants, including Lynch's wife, also were convicted in the U.S. District Court trial. Lynch, 36, has a home in Hillcrest Heights, Md.

The verdict, returned by the jury after two days of deliberations of the 26-count indictment involving 10 defendants, climaxed a 14-week trial during which about 120 witnesses testified about what was described as a multimillion-dollar drug operation that existed from 1972 through 1977. In courthouse circles the drug operation was dubbed the "fat lady ring."

Lynch, who faces a possible life sentence on the racketeering count, showed no emotion as the verdict was returned. The only defendant to be acquitted was Clayton Pina, a relatively minor figure in the case, who was indicted only on a conspiracy charge.

Although Lynch and other defendants were indicted for illegally obtaining and distributing Preludin - an amphetamine-and Dilaudid-a pain killer - the jury acquitted these defendants charged on the Dilaudid counts. In all, Lynch was convicted of 15 counts and his alleged principal assistant, Emma Jean Ward, was convicted of six.

The basic scheme used by Lynch was to recruit teams of overweight men and women and take them to physicians in six eastern cities-New York, Philadelphia, Atlanta, Miami, Birmingham, Ala., and Pittsburgh. They were taken by Lynch's lieutenants from one doctor's office to another obtaining prescriptions for drugs, occasionally stealing prescription pads and then filling out prescriptions, it was said.

The physicians visited were "walkins" who did not require prior appointments to treat patients. In some cases, the women involved returned in disguise-wearing wigs, glasses and different clothes-more than once during the same day to get prescriptions, the court was told.

Three physicians, who the prosecution charged wrote prescriptions they knew would be used for illegal purposes, were among 22 persons originally indicted in August 1978. The three physicians, along with nine others, have pleaded guilty and are either serving jail sentences or are about to be imprisoned.

According to testimony presented by the prosecution, Assistant U.S. Attorneys Peter O. Mueller and Charles R. Harkins Jr., Lynch paid $25 for every prescription that was obtained and filled. He then sold each individual Preludin pill, sometimes used by persons who want to suppress their appetites while on diets, for prices ranging from $4 to $12. Dilaudid pills allegedly commanded prices ranging from $25 to $35 apiece.

Lynch, who lived at 2424 St. Clair Dr., Hillcrest Heights, had no convictions before yesterday's verdict. According to several sources familiar with the case, Lynch lived an extravagant life-wearing pink suits, buying a $14,000 Cadillac that he had painted to match the pink of Preludin pills and paying cash for other cars and a business he secretly owned on Georgia Avenue.

Lynch used the Georgia Avenue store, Quality Market, and another store-Irvin's Variety-as locations for selling drugs under the counter, according to government sources. Although Lynch was represented during the trial by a court-appointed attorney, Mike Bailey, Lynch allegedly realized "millions" from his drug operation.

Lynch and his codefendants originally went on trial Oct. 31 before U.S. District Judge Thomas A. Flannery. That trial ended in a mistrial three weeks later after Flannery suffered a heart attack. A new trial was ordered over objections by the defense. The U.S. Circuit Court of Appeals upheld the new trial order and the Supreme Court refused to review the decision.

The second trial began on Jan. 25 before U.S. District Judge Louis F. Oberdorfer and proceeded at a glacial pace because of Lynch's refusal to allow evidence to be introduced by the prosecution without strict observance of formal evidentiary rules. As a result even minor evidence like hotel records required testimony from a witness who had first-hand knowledge of them and then possible cross-examination by 10 defense lawyers.

Besides Lynch, his wife, Myrtle (Sister) and Ward, the other convicted defendants are:

John W. (Sweetmeat) Bruner, of 912 4th St. SE, convicted of conspiracy and interstate travel in aid of racketeering.

Milton Battle, 1727 L St. NE, convicted of conspiracy and two counts of interstate travel.

Tryone J. (James or Little Jimmy) Johnson, 1242 Delafield P19 NE, convicted of one count of interstate travel.

Theresa Lucas, 4714 9th St., NW, convicted of conspiracy, illegal distribution of Preludin and two counts of interstate travel.

Thomas (Mr. Wonderful) McCloud, 100 56th P1. SE, convicted of one count of interstate travel.

James (Bim Bim) Thomas, of Washington, convicted of one count of interstate travel.

Oberdorfer set sentencing for the defendants for June 7. Carl Lynch, Ward and Thomas are being held in custody. The other defendants were released on bond or on personal recognizance.