San Francisco — Out of an undulating sea of plastic American flags a homemade sign popped up at the rear of the Pennsylvania delegation, hoisted high by a gray-haired woman in white suit and electric blue blouse. She pumped it up and down to the insistent beat of Michael Jackson's ''Beat It.''
Crayoned on the sign were four words: ''Traditional Values, New Perspectives.''
Those were, in fact, the twin themes implanted throughout last week's Democratic convention here.
How much the party and its point man, Walter Mondale, have moved on to new perspectives is open to question. Protectionist economic policy and uncritical conglomeration of pressure groups are still Mr. Mondale's approach.
But traditional values were evident from the opening keynote by Mario Cuomo, emphasizing family values and picturing the nation as a family of families, to the final medley of patriotic tunes and that moving blanket of bright-lit flags. Alongside family, hard work, and patriotism another usually Republican theme bobbed up frequently: back to basics in education. Fritz Mondale even got a rise from his audience when he said ''parents must turn off the television; students must do their homework.''
The convention, in short, played Capture the Flag with some of President Reagan's favorite teams. And the party that over the past two decades had played host to anarchic splinter groups suddenly was orderly and vehemently back to old values.
It's remarkable how the political system creates its own corrective pendulum swings. What happened in San Francisco's subterranean Moscone Center was not a reverse polarization of the epic type that occurred when the two major parties switched their 19th-century roles. But it was nevertheless striking. Toynbee or Darwin would see it as a natural response to shellacking at the polls. Just as Mr. Reagan proudly admits his debt to Franklin Roosevelt for the stimulus and techniques he used to reverse parts of the FDR revolution, so did Mr. Mondale admit that his party would adopt some Reagan slogans - strong defense, law and order, a growing private economy, etc. - in its attempt to undo the Reagan counterrevolution.
To all those lunchpail ethnics who deserted the Democrats in 1980, Mr. Mondale made a head-on appeal: ''I heard you. And our party heard you. After we lost ... we began asking you what our mistakes had been.''
It's obvious that the major electoral strategy of the Mondale-Ferraro team will be two-pronged:
1. Woo back those blue-collar deserters (largely in the Midwest and East) with the Cuomo-Ferraro team of family-work-law-and-order-get-ahead and an almost jingoistic pledge to protect American workers.
2. Register and goad to the polls new voters (women, blacks, Hispanics) by means of the Reagan ''unfairness issue.''
If the Democrats succeed in neutralizing Mr. Reagan's hold on the family-patriotism-back-to-basics issues, the election will likely focus more stringently on a battle of economic perception. Is the Reagan program just blatant reverse Robinhoodism? Is Mr. Mondale able to say ''no'' to any of the coalition of interests he has assembled, and thus cut the Reagan budget deficits he assails so vigorously?
The Cuomo and Mondale speeches at the convention were moving appeals to the best in America, but, faced with superdeficits, voters must attempt to put price tags on those speeches.
One of Mr. Mondale's recent vice-presidential finalists told me that the candidate has done just that, and is sorely aware of the difficulty.
He knows, for instance, that however important it may be to call for weapons cuts, weapons systems are only a small part of the Pentagon budget. Military pensions have to be looked at. So do government employee pensions in general.
Even the apparent Mondale forthrightness in announcing he will raise taxes and challenging the President to do likewise is somewhat elusive. The Democratic candidate does not say what taxes he will raise.
Economists advising Mondale on the deficit problem are understood to be studying such well-examined measures as a surtax which would repeal part of the Reagan tax cuts, and a delay or shaving back of indexing against bracket creep.
Probably the most interesting idea the economists have under their microscopes is a selective Value Added Tax plan (VAT). It probably would be given another name, since the acronym VAT is considered the kiss of death. What it would do would be to add a tax to all US manufactured items - except food, clothing, medicine, and services. Exports would be exempt. Imports of the same goods would be taxed. This would give the federal government new revenue, tax consumption of manufactured goods, protect Mondale union backers in basic industries, and create a bargaining tool to persuade European nations to lower their own VAT entry fees.
Another Mondale adviser says the candidate needs to do something - quickly - that is contrary to the interests of the AFL-CIO. Unless he does, says this adviser, voters will not believe his assertion that he, like Harry Truman, is able to say ''no'' to clamoring supporters.
At and before the convention, the adviser notes, Mondale's operatives didn't say no to anyone who yelped. Southerners got (to their bemusement) Bert Lance. Homosexuals got the power they demanded within convention committees, despite the pervasive family theme.