Federal prosecutors in Northern Virginia have begun a drive to deprive suspected drug dealers of their allegedly illegal profits by seizing their houses, offices, cars, mortgages, personal loans and antiques.

The U. S. officials invoked a 4-year-old law aimed at tracking illicit drug profits hidden in legitimate business ventures in moving against an alleged 20-member drug ring indicted this week in Alexandria.

The 1978 federal forfeiture statute, frequently employed by law enforcement officials in California and Texas, has been little used in the Washington area until now, according to Assistant U. S. Attorney Karen Tandy. She said the Justice Department recently has mounted a "tremendous push" designed to promote use of the law as an effective means to combat the country's widespread and highly lucrative drug trade.

In April, eight weeks before the indictments, the Alexandria-based prosecutors discreetly sought and won forfeiture of $1.8 million in U.S. District Court in North Carolina. The money, which prosecutors say was the fruit of the ring's alleged East Coast drug smuggling, had been loaned out to develop a portion of a prestigious resort at Hilton Head, S.C.

Prosecutor Tandy said yesterday federal officials have not yet tallied the dollar value of properties being sought or already seized. Tandy said prosecutors from across the country have telephoned to seek advice on how to carry out similar forfeitures in drug cases.

Business investments by the alleged ring, which includes two Washington area attorneys among the defendants, filled several pages of the 79-page indictment returned Wednesday in Alexandria. Prosecutors alleged the ring operated for nine years and realized profits "well in excess of $30 million," Tandy said yesterday.

Among the properties being sought by the government are an interest in an Annandale condominium building held by one of the lawyer-defendants, W. Stephen McConnell; 43 acres of land in Loudoun County; a Tysons Corner office building; several expensive cars; a Fort Lauderdale, Fla., home; promissory notes worth about $120,000, and a $225,000 mortgage loan to a Georgia development firm for 32 partially completed townhouses in Columbia, S.C.

Prosecution documents pictured the alleged drug ring indicted this week as being awash in cash revenues from illicit drug dealings. Ringleaders allegedly spent more than $600,000 on five ocean-going vessels and an airplane to import an estimated 130 tons of marijuana and hashish from South America. Tandy said a search warrant executed in April in Florida led federal tax agents to uncover a prized, yellow 1949 Rolls Royce purchased by one of the defendants.

Federal agents last fall seized a 10-acre Fairfax County home valued at up to $400,000, saying it had been bought with alleged drug profits by Leon Durwood Harvey, one of those indicted this week.

Some ring members, including Harvey, also are charged with offering up to $200,000 in cash bribes to prospective witnesses if they would leave the country or stand in contempt of court rather than testify to a federal grand jury investigating their alleged activities.

Tandy yesterday said at least seven of the defendants are believed to be living in Costa Rica. She later told a U.S. magistrate that some defendants remaining in the Washington area were recently contacted and offered free passage to Costa Rica if they would leave the United States before the indictment was returned.

Magistrate Quin Elson, rebuffing prosecution objections, yesterday reduced $500,000 bonds set Wednesday for two defendants. Joseph C. Blackburn of Madison County, near Charlottesville, Va., was freed on $25,000 bond. Bond for Wayne Scott Morris of McLean was reduced to $50,000. Morris remained in custody last night.

Morris' brother, James D. Morris, was arrested yesterday afternoon in Fairfax County. The two lawyer-defendants, McConnell and Arthur S. Meisnere, both are free on bond.

Arraignment is scheduled for July 9 in U.S. District Court in Alexandria.