The 1970s were tough on the older cities of America and on the Democratic Party that had its roots there. But here in Springfield, there is evidence that both may be recovering.

The city is flourishing. In the waning years of the last decade a combination of federal urban development action grants, state facility projects, private investments and historical preservation efforts transformed the downtown of a typically bleak old industrial center into an exciting mixture of old and new buildings, indoor and outdoor spaces, brimming with activity and full of people.

Last weekend, in the new civic center and its nearby hotels, more than 3,000 Massachusetts Democrats tried to come to terms with their heritage from that era: a fractured party and a reversal of political fortunes. If the evidence of the party's recovery is not nearly as conclusive as the revival of the host city, it still carries a message of hope.

The headline out of Springfield was that the Democratic state convention endorsed ex-Gov. Michael S. Dukakis, a liberal, over conservative Gov. Edward J. King, by a 2-to-1 margin. But the story is much more intriguing than that. It really was the first step in testing whether the differences of class and philosophy that split the Democratic Party here in 1978 and nationally in 1980 can be healed in the first election of the Reagan era.

The answer won't be known in Massachusetts until King and Dukakis fight it out in the Sept. 14 primary and the winner faces a serious Republican challenge in November.

The gubernatorial election here has important national implications, and not just because this is the home state of Sen. Edward M. Kennedy (D-Mass.) and a state that Ronald Reagan carried in 1980.

Mike Dukakis is often compared to Jimmy Carter, and the political failure of his first administration (from 1974 to 1978) was paralleled a bit later by Carter's failure on the national level. Like the former president, Dukakis is a man of high intelligence, scrupulous personal honesty, modest in his tastes and almost humorless in his purposefulness. His administration was characterized by its academic credentials, its devotion to fashionable economic, social and environmental goals and its political clumsiness.

He quarreled constantly with the Democratic legislature and ran into loud criticism from the left wing of his party for his efforts to economize. While attempting to quell that rebellion, he was ambushed in the 1978 primary by a rival who cut him off from the party's urban, working-class, Irish and Italian Catholic base.

King beat Dukakis on a Reaganesque set of issues: lower taxes, tougher welfare laws, the death penalty, an end to state-financed abortion. Like all civil wars, this one left a residue of bitterness.

One Massachusetts elected official told me before the convention began that "each side has utter contempt for the other." He likened it to the clash between Dick Daley's cops and precinct captains and Gene McCarthy's "flower children" in Chicago in 1968.

By that standard, the Springfield convention was a tea party. The King camp, which had lost the endorsement battle back in the February caucuses, kept its delegates on a tight emotional leash, while spreading the word that the convention was an effete conspiracy against the real Democrats of the state.

David L. Bartley, the brilliant and cynical former speaker of the Statehouse, who has helped to prop up King's faltering administration since he took over as temporary chief of staff a few months ago, dismissed the convention as the usual liberal "Chablis and Brie" crowd. There were a lot of teachers and public employees and suburban issue activists. But I also met retired icemen and firemen and office workers and a slew of members of the legislature Bartley once led. Wnalysis, hize, to undith Dukakis leading in the pre-primary polls, the judgment of the convention against King will be hard to ignore.

The Reagan angle in all this adds to the interest. King has been outspoken in his admiration of the president's economic and social policies--so much so that Bartley, worried about the Democratic primary, called publicly last week for the governor to "have a loud and public divorce" from the Republican president. But King, like Reagan, is stubborn in his convictions, and rejected Bartley's advice.

Dukakis' campaign strategists, Patrick Caddell and Robert Squier, therefore plan to run the primary campaign (and the general election, if they get that far) as a straightaway attack on the supporters of Reaganomics. That gives the president two chances to win in Ted Kennedy's home state--with King in the primary and with one of the three Republican contenders in November.

But if Dukakis can resurrect his career by regaining the urban, working-class support he lost four years ago, then the Massachusetts Democrats--like Springfield itself-- may conclude that the '70s were a time of renewal, and not, as it seemed, of ruin.