Maryland's numerous yet fragmented organized labor unions, labeled by one veteran politician the state's "sleeping giant," showed signs today of stirring to life.

More than 4,000 union members representing a broad and colorful slice of Maryland's beleaguered work force--from suburban Washington federal employes to Baltimore County steelworkers--buried their traditional factionalism for a Solidarity Day demonstration on the State House lawn. Their purpose: to remind Annapolis' predominantly Democratic legislators that Reaganomics stops at the Maryland line.

"On this day," cried out Thomas Bradley, Maryland-D.C. AFL-CIO president and organizer of the rally, "we call upon the Maryland General Assembly to show good faith to Maryland's workers and consumers by repudiating the Reagan economic philosophy."

Said Josh Williams, president of the AFL-CIO Metropolitan Washington Council, "We're trying to tell them legislators don't go jellyfish on us. The conservatives want Maryland. We want to keep Maryland."

With Maryland's workers being brutalized with 9.7 percent unemployment and a higher-than-usual level of antilabor rhetoric from conservatives in the General Assembly, the unexpectedly large turnout in a drizzling noontime rain seemed even more significant. In the past, organized labor, in effect torn between blue-collar unions and federal workers' unions, never was able to overcome its own divisions to galvanize its members into a statewide political force.

Annapolis city police estimated the crowd at 4,000, but rally organizers said they believed at least 10,000 participated.

"This is the biggest rally I've ever seen here," said a slightly stunned Del. Robert Redding (D-Prince George's) as he scanned the crowd.

"It really is the sleeping giant," Redding said. "During the economic growth years, the rank-and-file sort of drifted apart. I think maybe the unemployment rate and the other economic issues are starting to hit home. The effect is the same now on the federal worker as it is on the blue-collar worker."

Bradley said he also called for the rally to "put some emphasis" on labor's raft of legislation before this year's General Assembly. Those measures include an ambitious-sounding proposal now before the Senate to change the way occupational disease claims are settled by abolishing the controversy-ridden occupational disease board. Also included are some traditional labor-backed proposals, such as bills to increase the weekly unemployment benefits and to allow public employes to bargain collectively.

But besides those so-called "gut" labor issues, unions this year are taking the lead in a variety of social and consumer causes. At a time when many labor critics are urging unions to retrench and settle for fewer, more qualified victories, Bradley and others have come out swinging against a "workfare" proposal to make welfare recipients work, against corporate tax breaks, and against lifting the state's ceiling on usury rates.

Labor has traditionally not had much success here when it steered from the purely labor-related issues. But on those strictly union concerns, labor has always been able to draw from a bank of good will in a traditionally Democratic state. Maryland voted for Jimmy Carter in 1980. Its two U.S. senators are both rated high by labor. And Maryland is the southernmost state without a right-to-work law.

Labor as a political force has never realized its full potential in Maryland, because of its own regional divisions, because labor clout here has been concentrated in a few ethnic, blue-collar areas of Baltimore and the surrounding county, and because political power in Maryland for a long time was the purview of political "clubs" and machines.

"They just never had the kind of muscle that their numbers would indicate," said Democratic party activist Edmond F. Rovner, a former labor lawyer and arbitrator now working as an assistant to the Montgomery County executive. "Labor is as balkanized as the rest of the state."

Also, historical racial differences kept blue-collar union members and blacks apart in Baltimore, to the benefit of the political organizations. At today's rally, Del. Redding, a former electrical union member, said, "Look out there. Every group is mixed. It wasn't too long ago that unions were for white folks."