A coalition of AFL-CIO unions representing some 225,000 Washington-area workers announced yesterday it has targeted a Maryland senator from Prince George's County for defeat.

Joslyn Williams, president of the Metropolitan Washington Council, said the organization will work to unseat Sen. Thomas Patrick O'Reilly, 43, and elect Del. Robert Redding to the 22nd District seat because O'Reilly has been a foe of labor.

"He and Montgomery Sen. Larry Levitan are the worst in our jurisdiction," said Williams. "We went after O'Reilly because he was vulnerable." He said it is the first time he remembers the coalition targeting an incumbent.

The labor council, which comprises 65,000 workers in Prince George's County, will hold a breakfast meeting of several county unions today to discuss plans to aid Redding's Senate bid. Redding, 52, a delegate for 11 years and chairman of the county delegation, surprised Democratic Party regulars when he filed against the senator from his own district on the July 16 deadline.

O'Reilly, with the backing of the other Prince George's senators, is considered to be the favorite in the race despite the labor support.

"They would like to be able to run the General Assembly," O'Reilly said yesterday. "In many cases they do that, but they cannot do that with me."

O'Reilly acknowledged the unions would have "some impact," while Williams was confident the unions would make a big difference.

"We are going to make that district a test case. We have as much to prove as the doubting Thomases have to learn," Williams said.