Maryland radiation officials tested air, water and milk samples again yesterday and found "no detectable" indication that contamination from Pennsylvania's Three Mile Island nuclear is moving south.

Nevertheless, the Associated Press reported that Gov. Harry R. Hughes has told civil defense officials that they should prepare for the remote possibility that Pennsylvania residents living near the plant would be evacuated into Maryland.

Following a full day of environmental monitoring a spokesman for the Maryland Health and Mental Hygiene Department said, "We feel we're in real good shape. Our no detectable levels of radiation." An around-the-clock command post and laboratory has been processing the samples, said Henry Nathan, the spokesman.

Meanwhile, in Washington, two unrelated demonstrations resulted in four arrests after one group of four nuclear power protestors sat down in the tourist line outside the east wing of the White House at 11 a.m. and unfurled a banner saying, "Politicians, Profiteers, Nuclear Criminals."

Police said the protesters were from the Washington area and most affiliated with the Community for Creative Non-Violence. They were charged with unlawful entry and failure to leave, both misdemeanors.

Another group of six demonstrators from the Harrisburg, Pa., area, near the site of the Three Mile Island accident, was forced to disband as they carried placards and chanted on the sidewalk near the east gate of the White House at 2:30 p.m.

The group carried a 7-foot kite inscribing: "Nuclear Power Won't Fly," which they had attempted to enter in the Smithsonian Kite Festival being held on the Washington Monument grounds.