An Energy Department memorandum that shows the agency considered plans to fire a key witness at nuclear defense hearings has drawn sharp criticism from Rep. John D. Dingell (D-Mich.), who plans to investigate it.

Dingell, chairman of the House Energy and Commerce subcommittee on oversight and investigations, charged last week that the memo seems to show that DOE considered trying to fire John Hnatio "simply because he refused to participate in the department's coverup of appalling security lapses at the nation's most sensitive nuclear weapons facilities."

Hnatio, a security specialist in the DOE's Office of Safeguards and Security, was a key witness before the subcommittee during hearings Feb. 3 on security problems at nuclear facilities.

DOE officials declined comment.

Congressional sources said the Feb. 23, 1983 memo was written by Ann Lewis, administrative officer of the safeguards offices. It reads:

" Office director Robert O'Brien requested that I check with personnel to see if we could fire Hnatio in regard to statement in last paragraph," Lewis wrote.

It said Hnatio could be reassigned, as he requested, or he could be fired.

"If you want to fire him, start documenting records, establish good performance standard; if he is rated unacceptable, then he can be reassigned, down graded, etc.; if he continues to fail to follow instructions, can lead to dismissal -- after warnings, reprimands, etc.," it advised. It said the process could take six to eight months.

Dingell has ordered his staff to investigate the matter, saying he believed DOE misled the subcommittee when officials indicated they did not plan to retaliate against Hnatio for his testimony.