Gerard H. Arnaudet was named executive director of the $155 million New Bedford (Mass.) City Retirement System, effective in April. He replaces Robert Stanton, who left the system in November to become pension administrator at the $475 million El Paso (Texas) Firemen & Policemens Pension Fund. Mr. Arnaudet was executive director of the $95 million Weymouth (Mass.) Retirement Board; he resigned today.