Maryland Republicans received a blow to their hopes of holding on to the Senate seat of retiring Sen. Charles McC. Mathias yesterday when former United Nations ambassador Jeane J. Kirkpatrick announced that she would not be a candidate.

Kirkpatrick said she was "flattered" by the Maryland GOP's interest in her. "However, I shall not be a candidate for this office," she said.

"I sincerely believe that I can make a more substantial contribution to public discussion of major issues of foreign and domestic policy by continuing to write and speak about them than I could make by plunging into intensive concentration on Maryland's affairs," Kirkpatrick said in a statement released by her office.

Kirkpatrick was seen by the Maryland GOP as its best hope of retaining the Senate seat in a state where only 24 percent of the voters register Republican.

After hearing of Kirkpatrick's decision, state Republican Chairman Allan Levey said, "I'm disappointed. There's been a lot of disappointments lately. Right now we've got to sit back and let it sink in."

Other Republicans mentioned frequently as possible candidates in the race include James M. Beggs, director of the National Aeronautics and Space Administration, and Donald Devine, former head of the federal Office of Personnel Management. However, Beggs is little known in the state.

In addition, some GOP officials said Devine might be controversial because of the cutbacks he supported in the federal work force and because he withdrew his renomination to head OPM after a colleague testified at a Senate hearing that Devine had asked her to lie about one of his controversial actions at OPM.

Kirkpatrick is currently a senior fellow at the American Enterprise Institute. She writes a weekly syndicated column and also is writing a book.