The success or failure of Saturday's Solidarity Day rally will go a long way toward determining the future role of organized labor in the Democratic Party.

Although the Capitol Hill rally represents a coalition of groups in the first major organized protest of the Reagan administration's domestic policies, it is strictly labor's show. "It's all our people. It's all our money. It's all our time," notes an official of the AFL-CIO.

AFL-CIO President Lane Kirkland, stung by one congressional defeat after another at the hands of the administration, first proposed the idea last spring over the opposition of some of the federation's own member unions. Leaders of some of the nation's largest unions argued that September was too soon to attempt any form of massive protest against Reagan's policies. They said any protest rally should be held sometime next spring when the administration's budget cuts begin to affect the public.

For Kirkland and the nation's trade union movement, however, the current rally appears to be a crucial part of a broader plan to return to power within the Democratic Party.

With effective opposition to Reagan's policies almost nonexistent, labor wants to position itself as the rallying point for future opposition to White House policies. Union leaders fear they will lose the initiative if they wait until next spring as other groups affected by the budget cuts grow bolder.

"Right now we are the focal point around which the opposition is being built," says a federation official. "It's our coalition." And that's the way labor wants to keep it.

The other major part of labor's plan for its return to party prominence is money. Labor appears to be giving money to the Democratic National Committee this year in near-record proportions. A top political aide for one of the unions describes the contributions so far as "really heavy money." There are indications that labor will give more than $1 million to the DNC, which has a budget of slightly more than $7 million.

By making itself a major financial benefactor of the party and the public rallying point for Democratic opposition to Reagan, organized labor hopes to exert a heavy influence over the next Democratic presidential candidate. Earlier this year, Kirkland freely admitted that his goal was to increase labor's influence in the party. Specifically, he indicated that the AFL-CIO wants to change its traditional practice of staying out of presidential primary election campaigns.

Right after Reagan's inauguration last January, Kirkland said he was "exploring ways to get into the political situation in 1984 before the primaries get going." Equally important, he said, it was time to get the Democratic Party back into the mainstream. "I think I know what the mainstream is," he said. "I think we're closer to where the people are."

Becoming a power within the Democratic Party also is extremely important for Kirkland's own leadership position within the labor movement as the head of the giant labor federation. Kirkland's power is largely dependent on his ability to wield influence in government.

This was the strength of the late George Meany, who exerted enormous influence within government circles during his lifetime -- first at the state and then the federal level. Meany was a master at pitting the White House against Congress. Other union leaders had to come to Meany when they had a major problem with the White House.

But for most of his years in Washington, Meany had a strong Democratic base to work with in Congress when he was dealing with the White House, even when the White House was in Republican hands.

Kirkland does not have that luxury. Not only is the White House in the control of a Republican administration that will have little to do with him, but he also has no real congressional base on which to try to build his power.

Therefore, Kirkland has little choice but to try to become a major force within the Democratic Party if he hopes to wield the kind of power within the labor movement enjoyed by Meany.