A program to welcome street performers and musicians to Pleasant Street will be tried out on a pilot basis this summer. “Live performances make a positive contribution to the culture and ambience of Malden Square,’’ the city said in a prepared statement. The city has designated three spots on Pleasant Street as performance spaces, and will hold auditions to determine who receives permits. Current time slots stretch for four hours on Friday and Saturday nights. Performers also will be allowed to sell recordings of their performances. Those who want to audition should contact Kevin Duffy in the mayor’s office at 781-397-7000.