BALTIMORE, NOV. 12 -- A physician at the National Institutes of Health, charged Tuesday with selling narcotics prescriptions to undercover agents, was ordered held without bond today after a federal prosecutor argued that the doctor might leave the country if released before his trial.

Assistant U.S. Attorney Harvey Eisenberg told a federal magistrate here that Dr. George C. Daniel of Potomac, a research fellow at the NIH, lied Tuesday when he told arresting agents that he was a United States citizen, born in New York, and had assets limited to $3,500 in a bank account.

Drug Enforcement Administration agents who studied documents seized at Daniel's home have determined that he is a British subject, born on the Caribbean island of Dominica, and has been living in the United States on an expired student visa, Eisenberg told Magistrate Catherine C. Blake in U.S. District Court.

He said investigators also believe that Daniel, who is a licensed pilot, owns a Cessna aircraft, and that he recently recieved a $200,000 loan from a source Eisenberg did not identify. He said Daniel had made down payments on four to six real estate properties in the Washington area.

Daniel's exact age is unclear. Eisenberg said the documents show he was born in the late 1940s or early 1950s. He said Daniel graduated from Columbia University in 1975 and from Yale Medical School in 1979, the year his student visa expired.

Daniel, who attracted media attention last year with his plan for a new medical house-call service in the Washington-Baltimore area, was ordered held in the Baltimore City Jail, pending his trial on 11 charges of attempting to dispense a controlled substance illegally. If convicted, he could face up to 20 years in prison for each count.

A federal grand jury alleged that Daniel, between Sept. 15 and Oct. 30, sold 11 prescriptions for a total of 330 tablets of the pain-killing narcotics Dilaudid, Percodan and Demerol. Undercover agents paid $100 each for the prescriptions, according to the indictment issued last week in Baltimore and unsealed Tuesday.

Daniel, an endocrinologist whose three-year fellowship at the NIH was to end next month, began a business last year that he called Geodan Medical House Calls Inc. He said he had enlisted about 60 retired or moonlighting physicians to make house calls, primarily to handicapped and elderly patients who were to be charged according to their incomes.

Eisenberg said DEA agents plan a detailed review of the Geodan company's activity in the last year. State records show Geodan is an active corporation, and a half-page advertisement for the service appears in the Yellow Pages for Southern Maryland.