Ronald Reagan went out in the midday sun yesterday, returning to the scene of his inauguration to beat the drums for one of the most significant scams of his administration, the Constitutional amendment for a balanced budget.

None among the several thousand in his sweltering audience paid more rapt attention than the emergency medical teams hovering on the edges. They were watching for victims of the 92-in-the-shade heat.

The rescue workers hauled or wheeled away about a dozen casualties of the murderous sun and leaden air as the president called for "a new people's crusade" to stop government spending.

His listeners seemed to be fried government workers, baked employes of the Republican National Committee and tourists, who panted to the site for the windfall of seeing the president live.

It was a major production, with sweating White House advance men scurrying about, the Marine Band playing "Ruffles and Flourishes" and a heavy Cabinet turnout that included Secretary of State George P. Shultz, who could have been suspected of having better things to do as he assumes world burdens. Even Vice President Bush, whose campaign references to "voodoo economics" make him somewhat less than a natural for such events, was pressed into a rare public appearance. He wisely spoke of the weather.

Most of the mighty were in shirtsleeves. The president wore his jacket and bulletproof vest. While onlookers used their posters as sunshades and their tickets as tiny fans, a red-faced Reagan labored through a speech in which he promised to make good on a campaign promise to balance the budget--under certain circumstances.

Just before the rally, House Majority Leader James C. Wright Jr. (D-Tex.) called the president "the Babe Ruth of deficits." He was referring to the $104 billion difference between intake and outlay in the current budget. The Democrats want to blame it on Reagan's tax cuts and extraordinary defense spending. Reagan seeks to lay it on "big-spending Democrats."

Wright does not speak for all Democrats. Rep. William V. Alexander (D-Ark.) ruefully conceded that the idea of a balanced budget, easily understood in all households and approved by 31 state legislatures, is "irresistible" to politicians.

The division between two conspicuous California officeholders is illustrative of the election-year bind in which Reagan placed the Democrats. Senate Minority Whip Alan Cranston (Calif.), a candidate for president, is opposed. He believes that social programs dear to the Democrats will be more menaced than ever under the amendment. The exception to strict budget control, which can be voted by three-fifths of Congress, will be made for defense spending, he says.

But his California Democratic colleague, Tony Coelho, chairman of the Democratic Congressional Campaign Committee, is a cosponsor of the amendment. He contends that the social programs have sufficient constituencies so that the 60 percent of Congress needed to sanction overspending can be mustered to safeguard them, forcing a cut in the defense budget.

Unlike most of his Democratic colleagues, Coelho feels the coming debate will inevitably focus on the abject failure of supply-side economics. Other Democrats think Reagan wins every time he is talking about the budget rather than Reaganomics. Coelho thinks that Democrats cannot afford to vote against what so many Americans regard as "fiscal responsibility."

Chances for passage are excellent.

The president will emerge from the air-conditioned comfort of the White House later this week for another scam, this one in the foreign field.

At the Organization of American States tomorrow evening, he will attend a "gala Caribbean summer evening" to celebrate his Caribbean Basin Initiative, a move that permits him to avoid addressing the real problems of Central America, which happen to be injustice and oppression.

In announcing it last February, Reagan called it "an integrated program that helps our neighbors help themselves." What he meant is that these countries need only be introduced to the glories of the capitalist system and the free market place to escape the fate of becoming "new Cubas."

One tiny flaw in the grand design has emerged. The president has sharply limited the import of the Caribbean's major export, sugar, and those countries will lose millions in income under the new quota system.

But it will be a great party. Central American leaders, ambassadors and Cabinet members will turn out. Bands will play. Television cameras will be there.

But the Caribbean Basin Initiative and the balanced budget amendment illustrate one point: if you are not willing to admit what the trouble is, you are not likely to find the solution.