Jack E. Aalseth, who helped build ERC International Inc. into a major professional services firm before its acquisition earlier this year by Ogden Corp., is retiring as chairman and chief executive officer, the company said yesterday.

Aalseth, 57, founded Evaluation Research Corp., which became ERC International. He built it into a firm with $150 million in annual revenue, in part through skillful acquisitions, said Peter C. Keefe, an industry analyst with the investment research firm Johnston, Lemon & Co. in Washington.

"He grew the company very rapidly through the good defense years, and he showed some foresight in diversifying the company into non-defense activities when he did," said Jeffrey Berg, an analyst with Raymond James & Associates in St. Petersburg, Fla.

ERC International's professional services include defense contracting and biomedical research and development. One of the company's major diversifications was the creation of ERC Environmental and Energy Services Co., which is 69 percent owned by ERC, with the rest of its stock publicly held. Earlier this year, after ERC's acquisition by Ogden for about $80 million, Aalseth also retired from that company.

Aalseth said that after his retirement, which takes effect today, he will spend some time on a new 65-foot yacht. But he said he intends to stay active in the professional services area, within the limits of an employment contract with Ogden that bars him from competing.

He said he expects to join additional boards and to work in an investment banking capacity in mergers and acquisitions within the industry.

"There is a big need right now for small to medium-sized companies that are feeling the real crunch of changes in government spending patterns to make new alliances," he said.