Ronald Reagan, seemingly confident in his status as a frontrunner, yesterday refused to debate or engage in joint appearances with his GOP opponents on grounds such encounters would encourage "divisiveness" within the Republican Party.

"I would see no reason for debate between Republicans," Reagan said at a 20-minute news conference in the Senate's Dirksen Office Building. "I would welcome a debate, if I were the nominee, with members of the opportunity party."

Reagan's managers already have declined a debate in Iowa and turned down joint appearances in Texas and California.

Reagan's refusal to debate apparently was tied to a strategy that calls for him to behave as if he were already the Republican nominee, ignoring opponents within his own party and concentrating his fire on President Carter and the Democrats. A similar strategy worked for Reagan in 1966, when he paid no attention to a Republican opponent in California, won the nomination easily and defeated incumbent Democratic Gov. Edmund G. (Pat) Brown.

Part of the Reagan strategy is to produce a string of endorsements designed to demonstrate that he has appeal in the Northeast, where he was badly beaten by President Ford in 1976.

In Washington yesterday, the Reagan committee announced the backing of 30 members of the House and six of the Senate, most of them solidly conservative and 15 of them from California. Rep. Jack Kemp of New York was named chairman of policy development in the Reagan campaign.

In Boston, where Reagan arrived more than an hour late because of a mechanical failure on his chartered airplane, he accepted the endorsement of two of Massachusetts' six Republican state senators, Boston's only Republican city councilman and Anthony DeFalco, a major figure in Gov. John Volpe's administration in the 1960s.

The endorsements, while politically respectable, stopped short of conveying the impression of a Reagan bandwagon.

The traditional, anti-government Reagan emerged full force on the stump in Boston yesterday, contrasting with the more sedate candidate who officially opened his presidential campaign in New York City the night before.

Amid cheers, balloons, a band, and signs that said "Sink with Ted, Swim With Reagan" and "Forever Reagan," the candidate heaped scorn on a flock of federal policies and blamed government controls on the oil and gas industry for the energy shortage.

"I pledge to you I want nothing more in my life than to try not to run a massive government better, but to get that government out of the way, make it smaller and turn back to you the people the ability to do the great things you've been doing," Reagan said.

Kemp introduced Reagan at his Washington news conference as "the oldest and wisest of all the candidates [who] has embraced the youngest and freshest of ideas."

When Reagan, who would turn 70 within a month after becoming president, was asked whether he had the vitality to serve in the White House, he replied that the coming arduous campaign would be the test of that.

"I think the whole issue of my age will be resolved when the people of the country see whether I can go the distance," Reagan said. "If I were a betting man, I'd bet that I don't have to be helped off the track."

Reagan jabbed at Carter in his Boston speech, saying that a graduate of Annapolis was at the helm of the ship of state, but that the ship had lost its rudder. But in Washington he backed the president's actions in freezing Iranian assets and boycotting Iranian oil, saying that the situation was too sensitive for partisan comment.

Later in the day, in Manchester, N.H., Reagan's campaign manager, John P. Sears III, said Reagan's refusal to debate was not absolute. He said Reagan would look at invitations "on a case-by-case basis" as they come along.

Reagan's campaign organization issued a statement by his doctor saying Reagan is in good health. The statement said he had prostate surgery in 1967 but that there was no sign of cancer. He also has a history of minor respiratory allergies and arthritis in his right thumb, according to the statement.