Sen. John C. Stennis (D-Miss.) warned his Senate colleagues yesterday that an overly tough ethics code could make a good senator hard to find.

Stennis, appearing before a Senate committee drafting an ethics code, said an overly tough code could "clothe" a senator "in so many restrictions that he becomes just like a civil servant."

Stennis quickly added that his comment was not meant to denigrate the nation's 2.8 million federal civil servants. Indeed, he said, civil service employment is a noble calling.

But, Stennis said, the Senate attracts men with "broad experience." They are men of "character, experience and competence," he said.

Placing too many restrictions on them "will just scare them away," Stennis testified.

The senator said he believes his colleagues should be required, on a limited basis, to disclose their incomes. He also said he would be in favor of restricting outside employment that clearly conflicts with senatorial duties.

But he asked the committee not to go overboard in its zeal to correct present or future unethical conduct.

"My last point," he said in a prepared statement, "is to caution you not to believe that you can come up with a code that will be the panacea of all ethical evils.

"No matter how perceptive and farsighted you are, unforeseen situations will arise in the future. If that happens the Senate will not be helpless, for perhaps our highest calling is our collective conscience."

Stennis was one of five witnesses to appear yesterday before the panel, which has until March 1 to produce a proposed code of ethics for Senate consideration. The panel is chaired by Sen. Gaylord Nelson (D-Wis.).

The other witnesses yesterday were Sen. Howard W. Cannon (D-Nev.) and William D. Hathaway (D-Maine), James C. Kirby Jr., a New York University law professor, and former Commerce Secretary Peter G. Peterson.

Peterson, who recently called for a code of ethics for all federal executives, recommended that the senate include "highly visible" enforcement procedures in any code it adopts.

"If somebody doesn't get into the business of public auditing and reporting, the job's not even half done" in developing new standards of senatorial conduct, Peterson said.

Cannon, chairman of the Senate Standards and Conduct Committee, and Hathaway agreed with Peterson's remarks.

"There is little doubt that the time has come for a greater degree of personal financial disclosure than we have now," Cannon said.

However, like Peterson, he said he saw no practical value in requiring senators to publicize their income tax returns. Making public income taxes would fail to disclose any real or potential conflicts of interest, and would only constitute "an unwarranted invasion of privacy," Cannon said.

Hathaway said "complete financial disclosure" is needed in the Senate because "public distrust seems to be centered on the belief that some of those in public life have something to hide."

"We can correct this view by simply requiring complete annual disclosure of the amounts and sources of incomes and other assets and making that data available in the public," he said.

Kirby recommended that the Senate establish a commission, "including a minority of members from the public," to implement the new code, once it is approved.

Kirby, who served from 1967 to 1970 as executive director of the Special Committee on Congressional Ethics for the New York City Bar Association, said the public members need not have voting power. "Ultimate disciplinary power in individual [ethics] cases would still rest with the full Senate," he said.