President Reagan announced yesterday that he is nominating former House member Mark D. Siljander (R-Mich.), defeated in a controversial campaign in 1986, to be the alternate representative on the U.S. delegation to the U.N. General Assembly.

Siljander, 36, has been working as a consultant in Washington since leaving Congress. He represented Michigan's 4th Congressional District from 1981 through 1986, when he was upset by challenger Fred Upton in the Republican primary.

He has conceded that his defeat was due largely to a tape he sent to ministers throughout the southwest Michigan district asking them to "break the back of Satan" by backing his reelection bid.

"In order to break this confusion, the smears, the attacks, the impugning of my integrity during this campaign, coming up on Aug. 5, this all-important primary, we need to break the back of Satan and the lies that are coming our way," Siljander said at the time.

Some supporters alleged that Siljander's primary election defeat was an example of anti-Christian campaigning.

Siljander is a "born-again" Christian and staunch Reagan supporter. He had served in the 4th District since 1981 when then-Rep. David A. Stockman gave up the congressional seat to become director of the Office of Management and Budget.