Agents of the U.S. Immigration and Naturalization Service staked out a downtown Washington apartment-hotel yesterday and arrested 94 persons as illegal aliens.

It was the biggest roundup of illegal aliens ever in the Washington area, INS officials said.

The arrests were made in the lobby of the Annapolis Towers at 1111 H St. NW, during a three-hour surveillance late yesterday afternoon, according to Russ Parry, supervisor of the INS criminal investigations division.

Parry said the agents took 104 persons into custody but released 10 of them after they produced proof that they are living in this country legally.

Parry said 41 of the 94 persons arrested admitted their illegal status and were bused last night to New York, where they will be deported after processing today.

INS agents were interviewing the remaining 53 persons last night at INS headquarters at 1025 Vermont Ave. NW, Parry said.

Parry said the INS detention center is not large enough to hold the aliens and that suburban police offficials were asked last night to take some detainees. Parry said the D.C. Jail, which normally holds arrested aliens, was too crowded to take the overflow.

Agents said the roundup at the hotel was carried out by 13 INS agents assisted by city police. The arrests were made quietly as the suspects were either entering or leaving the building, and there were no incidents, he said.

Parry said the arresrs came after several months of investigation. He said the hotel had been used as a "drop house" for newly arrived aliens and as a residence for some of them without the knowledge of the hotel management. The INS had "the full cooperation" of the hotel owners in the investigaation, Parry said.

Agents learned about the hotel from previous investigation and from a number of telephone complaints from other residents at the hotel, Parry said.

Most of the 94 aliens-of whom 10 are women-were employed in area restaurants, Parry said. He said a majority appeared to be from El Salvador and othe Central American countries. A few of the aliens were from Iran and Thailand, Parry said.

Parry characterized the arrests as the "biggest single one-shot" operation in the Washington area. Other long-term investigations in rural areas of Maryland's Eastern Shore have netted large numbers of illegal aliens, Parry said, but these were made in a series of roundups.

The largest previous roundup of illegal aliens in the immediate Washington area occurred in 1976 when 58 were arrested at an ice cream distributing company in suburban Maryland where most of the aliens worked as street salesmen.

The following year, 20 aliens were arrested in Washington during a soccer game that included mostly illegal aliens on the two teams.

In November of last year, 11 aliens were arrested at Blackie's House of Beef restaurant where they had been employed as kitchen workers.