As the fiscal 1984 budget battle gets under way in Washington, President Reagan's ''mandate'' from the American people appears to be more fragile than ever.
Political analysts still affirm that the 1980 and '82 elections endorsed change from earlier policies. But they emphasize that those elections did not endorse a particular economic doctrine, political philosophy, or party line - and specifically not Reagan's.
''Americans . . . are receptive to change but unsure about what is needed,'' observes political analyst Everett Carll Ladd, director of the Roper Center, an opinion polling organization. ''All during the 1982 campaign, this ambivalent electorate said it needed more time to reach a verdict on Ronald Reagan and his administration.''
At the halfway point of his administration, time has not run out for Reagan. Yet Reagan's new budget sends signals that conflict with earlier presidential statements, and this is likely to heighten the public's ambivalence.
In 1981, Reagan promised in his budget message: ''The economy itself should break out of its anemic growth patterns to a much more robust growth trend of 4 to 5 percent a year. These positive results will be accomplished simultaneously with reducing tax burdens, increasing private saving, and raising the living standard of the American family.''
In his new budget, he acknowledges ''mounting federal deficits . . . threaten the renewal of economic growth.'' And the new ideals of the Reagan budget are greatly scaled down: ''It must be bipartisan. . . . It must be fair. . . . It must be prudent. . . . Finally, it must be realistic. We cannot rely on hope alone.''
Democrats sense the new vulnerability for Reagan.
''He had a sense of clear vision and direction going for him his first two years,'' says Stuart Eizenstat, chief domestic adviser under President Carter. ''But now what's the agenda? We're for keeping our tax cut, but we're for more taxes in the future. We're for more defense, but not for as much defense as we were. We're for domestic cuts, but we still want to have jobs training and education. There is not a clear sense this is a program to take us out of our quagmire.''
''It's typical of what happens to presidents by their third year,'' Mr. Eizenstat says. ''Their programs have been battered and torn by reality. They end up having to compromise and lose the clear sense of direction they had when they came into office.''
The issue of fairness - favoring defense over social needs, the well-to-do over the needy - will cause particular problems for Reagan and the Republicans because of the new budget.
''You've got a 9 percent real increase in defense and a 3 percent real decline in domestic spending,'' Eizenstat says.
''Reagan's going to get hit on the equity-fairness question all over again,'' says Peter D. Hart, a Democratic pollster. The public is going to find out the budget freeze is a freeze on 'us' and not on 'them.' '' ''The fairness and compassion issue is already ours (the Democrats') as an issue.''
The fundamental American ambivalence about policies - tolerating both liberal and conservative solutions and goals - buys time for Reagan. But public refusal to be doctrinaire poses immediate problems for him, too.
For example, the American public by a margin of 3 to 1 wants a big federal jobs program even if it means adding to the budget deficit, according to a mid-January New York Times/CBS poll. ''On the budget in general,'' the survey's analysts conclude, Reagan emerges ''at loggerheads with public majorities on unemployment as well as the other key issues of social spending, military spending and tax policy.''
Congress clearly senses that Reagan has failed to convert the public to his set of economic principles, and it feels less constrained as the fiscal '84 budget cycle begins. Members of both parties note that the first Reagan budget message was full of certitude. Two years later, they see Reagan's budget writers blaming faulty economic assumptions for disappointment with results.
Like the public, Congress is in a wait-and-see mood.
''So much depends on events of the next months and year,'' says Thomas Mann, executive director of the American Political Science Association and a congressional affairs expert. ''In the House races for '84, there is no clear advantage for one party or the other.''
''It is foolish to talk about another failed presidency,'' Mr. Mann says. ''Reagan is in no worse shape now than at key points in 1982. The new problems are the long-term deficits, which will likely have a temporary effect on members of Congress.''