When the Democrats left here Sunday at the end of their mid-term national party conference, they had achieved what Lynn Cutler of Iowa, their vice-chairman, had defined as the minimal goal. They formed the firing squad in a straight line against the Reagan policies instead of a circle aimed at each other.

For a party that has been notably short on civility in recent years, it was a considerable achievement that there were no self-inflicted wounds.

Quite a few good rhetorical shots were landed. The speaking honors went to Sen. Ted Kennedy and former vice president Fritz Mondale. But neither of them was really able to answer the most important question about the Democrats: are they ready to be a national party again?

Kennedy and Mondale are liberals of the old school, which is natural and safe if you come from Massachusetts or Minnesota, as they do. In those states, Reagan got less than 43 percent of the vote in 1980, and voters seem tired of the conservative governors they elected just four years ago.

But Rep. Steny Hoyer of Maryland, a shrewd politician with the border-state mentality, made the pertinent observation. "You can't elect a president between Massachusetts and Minnesota," he said. "You have to be able to move south and west, as well."

That is an obvious fact of life for a party that won narrowly with a southern candidate in 1976 and lost overwhelmingly when that southerner, Jimmy Carter, carried nothing in Dixie but his home state four years later.

Yet southern accents were not prominent on the Philadelphia convention podium. One Dixie presidential hopeful, Sen. Fritz Hollings of South Carolina, rushed through his speech. The other, former Florida Gov. Reubin Askew, declined to speak at all.

(Askew's silence should not be mistaken for indifference. In fact, he is waging an intense underground campaign, reminiscent of Carter's outsider assault on the 1976 nomination. Without publicity, he has been in all 50 states since Jan. 1. He and his wife will "vacation" for 10 days this summer in New Hampshire "just to get the geography in our heads," he says, "and learn how they pronounce the names." If he carries his own garment bag, Carter-style, the other guys might as well concede.)

But there were a few southern speakers, and what they said serves as a useful correction to the current Democratic euphoria. Their message was that the voters rejected the Democratic Party's national leadership in 1980 for good cause and have yet to be convinced that Democrats have recognized the errors of their ways.

"The American electorate," said Rep. Kent Hance of Texas, "didn't feel the Democratic Party deserved its vote in 1980." Now his constituents are asking, "Where is the Democratic alternative to Ronald Reagan and his Republicans? Why hasn't the Democratic Party stepped up to the critical issues of the day with responsible alternatives? Why are we satisfied with simply attacking Ronald Reagan for the sake of attack?"

Hance's testimony was dismissed by some as the rationalization of a "Boll- Weevil" who gave Reagan big help on the 1981 tax bill. But the message was no different, in essence, in the speech of Rep. James R. Jones of Oklahoma who, as chairman of the House budget committee, has seen the nominal Democratic majority splinter on each key roll-call.

Jones warned that Democrats have lost control of "the vital center" of politics, and instead have been perceived as "the party of factions."

That was also the theme of loyalist Rep. Gillis Long of Louisiana, chairman of the House Democratic caucus. "Let us not kid ourselves," Long said. "The opportunity we have today comes not because of what we have done, but because of Republican failure. . . . The Republicans have given us a reprieve. They have embraced a program every bit as radical as anything factions of our party embraced during the 1970s."

To profit from the reprieve, Long said, "we must demonstrate to the American people that the Democratic Party we ask them to vote for in 1982 is a different party than the one they voted against in 1980."

Are Democrats doing that? All the southerners hinted that the answer is no, but Hollings said it bluntly. "On the all-important issue of the economy," he said, "the people still shy away from us."

"If Democrats cannot act for the common good to put America back to work, then we will not be entrusted to lead," he warned.

In Philadelphia, those southern voices were no more than a solemn counterpoint to the cheers for Kennedy and Mondale. In 1984, they will not be so easy to ignore.