Richard P. Sullivan, the former president and chief executive officer of Easco, a Baltimore tool maker and metal producer, said yesterday he plans to run for the Republican nomination for the Senate.

Sullivan, 52, who has never run for office, said he will make a formal announcement sometime next month.

While three Democrats already have announced for the seat of retiring Sen. Charles McC. Mathias Jr. (R-Md.), GOP officials have had problems recruiting a credible candidate to run in Maryland, where Democrats hold a 3-to-1 registration advantage.

E. Brooke Lee, a mayoral candidate in Washington in 1982, and Abraham H. Kalish have formally announced, but are considered longshots. White House director of public liaison Linda Chavez is considering a Senate bid and is expected to announce her decision in February.

Sullivan, who had been an executive at Easco for 20 years, left the tool firm in July after company officials lost a hostile takeover bid by Equity Group Holdings, a District-based firm with real estate and manufacturing operations.

"I concluded that I had run a big company and didn't want to do that again," said Sullivan. He said he has raised money for the Republican Party but has not been active in Maryland GOP politics.

GOP officials said that Sullivan's business credentials would be an asset and that he might be able to bring substantial amounts of money to his campaign. But they also said the fact that Sullivan is unknown both to GOP regulars and to the general public could pose a serious problem.