Army intelligence agents have spied on Sen. Adlai E. Stevenson IH, former Gov. Otto Kerner and about 800 other civilians in Illinois alone, Sen, Sam J. Ervin Jr. said yesterday in Washington.

Ervin, a North Carolina Democrat who heads the Senate subcommittee on constitutional rights, said his information was supplied by a former Army agent who was assigned to political surveillance in Illinois.

Investigated in Office

"The Army investigated these men during their campaigns for office and while they were in office," said Ervin.

Aside from Stevenson and Kerner, Ervin said, the Illinois target list of the 113th Military Intelligence Group-with jurisdiction over the Midwest-included Democratic Rep. Abner Mikva and a host of state and local officials, political contributors, newspaper reporters, lawyers and church figures.

Who Did It?

Stevenson told a reporter Wednesday he felt he was being observed on several occasions during this year's campaign. But he thought then the mysterious photographers with telephoto lenses were from the opposite political camp.

Now, he said, he doesn't know whether the alleged spying was "by the political opposition in Illinois, by the military or by whom."

Mikva told the House that if the reported practice is widespread "we have reached a frightening state against civilian control over the military."

Identified

The Senator did not identify his informant but the Washington Evening Star said he is John M. O'Brien.

The newspaper reported O'Brien identified himself in an interview as a domestic spy for the Army and said of his activities:

"The Army wanted to determine their political views so that in certain situations we would know how they would react; whether they would condone violence or be for non-violence."