The Sandinista government has barred an American Roman Catholic priest from returning to Nicaragua, where he has lived and worked for 12 years, a church spokesman announced. The priest, identified as Father Everett Brown, is the third cleric forced from or kept out of Nicaragua in the last 2 1/2 months. Father Uriel Reyes, spokesman for the Nicaraguan Catholic Church, told reporters that Brown was barred on Tuesday when he attempted to return from vacation. Reyes said he does not know why Brown was barred. An Interior Ministry spokesman said he had no information on the report.