Local independent record promoter Joseph Isgro and Polygram Records announced a settlement in Isgro's antitrust lawsuit against the record company. Terms were not revealed, but Isgro said in a telephone interview that they involve Polygram paying him an undisclosed sum of money. Isgro filed the $25-million action in April, 1986, two months after all the major U.S. record companies announced they were discontinuing the use of independent promotion because an NBC news broadcast had linked Isgro to organized crime--allegations the promoter vehemently denies. Isgro's suit alleges that 11 major record companies and their trade organization, the Recording Industry Assn. of America, conspired to put him out of business following the news report. Polygram is the third company to settle with Isgro, joining Capitol Industries-EMI and Motown. The remainder of the case is to go on trial in U.S. District Court in Los Angeles in February.