MIAMI (AP) _ Supporters of Nicaraguan rebels hurled eggs, rocks, a hammer and other debris at a smaller crowd of anti-Contra protesters Saturday as police in riot gear struggled to separate the competing rallies.

Elsewhere in the nation, more than 2,600 people, some with peace signs painted on their faces, rallied against President Reagan's proposal to fund the Contras.

No one was seriously hurt in the Miami incident, but police arrested one man and charged him with disorderly conduct after hundreds of pro-Contra demonstrators broke through a police barricade, said Miami police spokesman Juan Santos.

An anti-Contra demonstrator was rescued by mounted police after he was slightly injured in an attack by a swarm of pro-Contra demonstrators.

Cans, pieces of wood and other items flew over the heads of police from a crowd of 2,000 demonstrators favoring Reagan's proposal toward a group of about 200 non-interventionists across the street.

''This is the United States of America,'' said Jack Lieberman, a spokesman for the Coalition for Non-Intervention in Central America. ''We're not going to be intimidated by a bunch of thugs.''

Miami Mayor Xavier Suarez addressed the pro-Contra rally before the trouble broke out, and later walked through the angry crowd attempting to calm tensions.

In Boston, about 2,500 people rallied against the proposed Contra aid Saturday and called on the U.S. government to leave Nicaragua alone.

''We're claiming we have to contain a tiny country,'' said Noam Chomsky, a Massachusetts Institute of Technology professor who addressed the crowd. ''But this is insane. We should not be giving aid to the Contras at all.''

Chomsky said the purpose of the rally was to ''educate Americans so they can see it's not how much aid we should send to Nicaragua, but whether we should send aid at all.''

Vicki Lewis, a member of the group Pledge of Resistance who has visited Nicaragua twice, said she was at the rally because ''we have no right to interfere with Nicaragua's right to self-determination as a nation.''

Reagan's proposed $100 million aid package for the Contras was voted down in the House of Representatives last week. It goes to the Senate Monday for debate.

In his weekly radio address from Washington on Saturday, Reagan lauded the Nicaraguan rebels as men of ''blood and courage'' and demanded that the Senate resurrect the proposal.

Another Nicaragua protest held in downtown Salt Lake City, Utah, Saturday attracted more than 150 people.

''It's disturbing that the entire Utah (House) delegation voted in favor of aid,'' said Bruce Plenk, one of the organizers of the demonstration.

One sign at the demonstration said ''Not another Vietnam,'' while another proclaimed ''Kill hunger, not people.''