John F. Collins, mayor of the new Boston, declared war on old Boston politics Friday night at the Democratic Pre-Primary Convention. In doing so he set the theme for this summer's Democratic Primary campaigns.

Collins, who lost the convention's endorsement for the U.S. Senate to former governor Endicott Peabody '42, on the first ballot, told the delegates in his concession speech that "I have learned tonight, and indeed the hard way, that you can't always win when fighting power politics, "

"I concede in all honesty and candor that tonight Johnny Powers has had his night of revenge--it was long time in coming but it came."

John E. Powers, clerk of the Supreme Judicial Court and former president of the Massachusetts Senate, was Collins' unsuccessful opponent in the bitter mayoralty contest of 1959. Collins' slogan then was "Stop Power Politics."

The Mayor's daring charge that Powers was responsible for Peabody's successful nomination attempt was not just a hasty remark; it was part of a prepared text and part of Collins' strategy.

Essentially Collins is trying to strengthen his image as an apolitical, professionalistic administrator and mayor. And charging that the "bosses" are against him seems to be the easiest way to do this. Collins' strategy recognizes the growing electoral strength of the young, well-educated suburban voters who have abandoned city life.

Because he has never run for statewide office before, Collins is not well known in Massachustts' western cities and cannot rely on them to carry him through the primary. And the shrinking Boston vote, which is not completely Collins' because of his urban renewal position, is no longer a guarantee of nomination.

Many suburban voters think highly of Collins because of his stand on urban renewal and his stand on urban renewal and his opposition to the Boston School Committee and Mrs. Louise Day Hicks.

The entire campaign could become a battle between "reformers" and "pols" if P. Kenneth O'Donnell '49, candidate for the nomination for governor and Robert DiGiacomo, who is seeking the nomination for attorney general adopt similar charges, and if John L. Saltonstall '38, a Boston lawyer, decides to seek the Democratic nomination for attorney general.

Some of O'Donnell's sides charged that the convention was a "tarce." They claimed that many people at the convention were required to commit their votes to the choices of local politicians who controlled the selection of delegates.

DiGiacomo, a former assistant attorney general who was active in ferreting out corruption in state government, has based his campaign on dissociation with the party regulars.

Saltonstall, whose name is magic in Massachusetts politics, has never sought high political office before. But, he supposedly is disenchanted with the convention's endorsement of former lieutenant governor Francis X.