The Justice Department alleged yesterday that chemical wastes from a disposal site near Love Canal have entered the public drinking water of Niagara Falls, N.Y., and may present an imminent and substantial danger to public health.

The department's claim was contained in a series of legal papers filed in U.S. District Court in Buffalo. The claim added new complaints to a suit filed by the department Dec. 20, 1979, against Hooker Chemical and Plastics Corp., the predecessor to Occidental Chemical Corp.

The suit, which involves the S-Area landfill, was one of four filed against Hooker. One has been settled and Occidental and the government are negotiating the others.

The state of New York in October found, for the first time, that the city's drinking water contained trace elements of the same chemicals found in the landfill, about five miles from Love Canal, and that they probably came from there. The water, the state said, was "subject to dangerous pollution so as to constitute a menace to public health."

The city was ordered to prepare a plan for using an alternate source of water and to test the water daily. The city has switched to using another intake pipe, which it says reduces the S-Area contamination by about 90 percent.

The federal government also claimed in its papers filed yesterday that contamination of the groundwater supplying the Niagara Falls drinking water treatment plant, which serves 86,000 people, also comes from an old city-owned dump used from 1930 to 1950 for waste disposal. The treatment water plant was built over part of the site of the dump.

A class of chemicals called polynuclear aromatic hydrocarbons not used by Occidental is contaminating groundwater at the treatment plant from the old city dump site, the government charged.

The government said that from 1947 to 1975 more than 63,000 tons of chemical wastes, including some chemicals thought to cause cancer, birth defects, mutations and other illnesses, were dumped in the S-Area landfill.