A broad-based national coalition of organized labor and civil rights groups is expected to draw more than 100,000 marchers here on Saturday for a "Solidarity Day" rally to protest Reagan administration domestic budget-cutting and assert that they are still a major force in national politics.

The coalition of more than 200 organizations, pulled together primarily by the AFL-CIO and its network of local unions throughout the country, plans to have protesters march from the Washington Monument grounds to the Capitol for a two-hour rally.

The rally, in the planning stages since last May, was inspired in part by the union Solidarity movement in Poland, AFL-CIO president Lane Kirkland told organizers last week, but was fueled chiefly by Reagan's budget victories in Congress that have scuttled "50 years of progress and social programs."

President Reagan will not be in town Saturday. White House officials acknowledge they purposely sought a speaking engagement in Denver for Reagan to avoid the demonstration here.

Union workers in cities throughout eastern and midwestern parts of the country as well as chartered bus and train coordinators and veteran National Park Service officials say the buildup for the rally indicates it will be one of the largest here in years.

Union organizers claim they have 3,000 buses already lined up. Greyhound confirmed it has laid on at least 550 buses -- more than for any other single event for which it has provided transportation -- and Trailways indicated it has another 400 buses set aside. Greyhound said its buses have been chartered by Solidarity Day rallygoers from 57 cities in 21 states. Amtrak said it is scheduling a dozen special chartered trains to Washington along the Boston-New York-Philadelphia corridor, and said regular passenger reservations to Washington are running above normal for the weekend.

Union officials have begun a final week of intensive preparation, including mass leafleting in the Washington area and other major east coast cities.

AFL-CIO officials declined to say how much money has been spent on the rally so far and said no total budget was set for the operation begun last May.

Among major expenses was $65,000 to lease Metro's subway from 8 a.m. to midnight Saturday to allow rallygoers and ordinary subway passengers alike to ride without charge.

The American Federation of Government Employees has bought about $8,000 worth of radio advertisments to air on Washington stations this week. The AFL-CIO also produced a slick, 16-millimeter film on Solidarity Day that has been shown to groups across the nation.

The recent air traffic controllers strike forced sympathetic organizers to cancel more than 50 chartered flights for the rally, but bus and train charters absorbed much of the demand.

D.C. police and U.S. Park Service officials said special parking restrictions will be in effect in the rally area and encouraged participants and tourists to use the subway instead of driving to the Mall.

Organizers said a possible strike by District of Columbia hotel workers this week would have little effect on the one-day rally since most participants are expected to arrive Saturday and leave the same day.

March officials said area churches are being contacted about providing emergency shelter for those few demonstrators staying overnight, in case of a strike.

A variety of labor, civil rights and community activists is scheduled to speak at the rally, but organizers said no elected public offficials will address the crowd except D.C. Mayor Marion Barry, who will welcome the demonstrators to Washington.

Among the diverse groups participating are the National Gray Panthers, the Association for Retarded Citizens, Citizens for Tax Justice, several gay rights groups, Congress Watch and the Paralyzed Veterans of America.

Special sections of the monument grounds have been set aside for larger groups such as the United Auto Workers and the International Association of Machinists, each of which is expected to have up to 10,000 persons behind its banners.