About 300 supporters of President Reagan staged a rally on the lawn of the Federal Building in Westwood to show their approval of the Administration's policy on Nicaragua. The speakers included U.S. Rep. Robert K. Dornan (R-Garden Grove), Los Angeles County Supervisor Michael D. Antonovich, Bruce Herschensohn, a television commentator and former U.S. Senate candidate, and numerous leaders of primarily Cuban organizations. Patrick J. Buchanan, the president's outspoken communications director, was scheduled to speak, but an emergency in Washington prevented his appearance, rally chairman Gus Brado said. About 200 critics of Reagan's Central American policies staged a counter-protest along Wilshire Boulevard--across the street from the rally. Federal police had to break up skirmishes between the groups at least twice.