The Miami Herald, largest newspaper in a state that both major party candidates consider crucial in the November election, yesterday endorsed independent candidate John B. Anderson, saying "something is . . . dreadfully wrong when convential two-party politics produces choices as unacceptable to so many millions of Americans as a Jimmy Carter versus a Ronald Reagan."

The Herald, a morning paper owned by the Knight-Ridder Newspapers group which endorsed Gerald Ford in 1976, said in an editorial that "Mr. Carter's capacity to guide the nation has been tried these past four years, and it has been found wanting" despite some successes. The paper said voters should reject Republican candidate Reagan, "unless one believes, with him, that the future lies in a return to the past."

Florida's 17 electoral votes went to Carter in 1976, but a recent poll by four Florida newspapers (not including the Herald) showed the president and Reagan in a dead heat with 38 percent each. The Reagan campaign's polls show Reagan with a slight edge.

Anderson is doing poorly in Florida -- the Florida newspapers' poll showed him with the support of only 8 percent of the voters -- but the Herald advised readers to "not be misled" by Anderson's recent decline in public opinion polls. "They may be in large part an artifact of his inability to buy TV exposure, not a measure of the support he would have if noncommitted or fencesitting voters thought he could win," the editorial said.

The Miami News, the evening newspaper owned by Cox Newspapers, earlier endorsed Anderson.

The Philadelphia Bulletin endorsed Reagan yesterday as a "tough, determined, practical candidate."