In an empty city classroom, T.C. Greene, a street official of of Baltimore's CETA jobs program, is trying to advise 19 men and women, many of whom have never faced a job interview, on how to survive in the Reagan era.

"How many ex-cons have I got?" she calls out. Five men raise their hands.

"Okay," says Greene, in a style combining teacher, preacher and jazz performer, "you've got to just-ti-fy your neg-a-tives. 'Yes, I have been incarcerated, but now I have developed a positive life style. One of my goals is to maintain that life style. That is why I am seeking employment.'"

Each week more than 200 former employes of CETA, the federal jobs program being eliminated as part of President Reagan's budget cuts, have been attending crash courses like these to learn how to make themselves desirable to private employers. But despite its spirit, the session has the look of a no-win operation.

By May 1, about 1,000 CETA employes in Baltimore will have lost their jobs; by June, the number will have grown to 3,000 and city officials say they will probably be able to place only about a third of them. In a city where 26,000 turned out last year to compete for 70 openings for entry-level jobs at the Social Security Administration, the impact will be sharp and immediate.

While most proposed cuts are still being debated in Congress, the elimination of the CETA program has already taken effect through executive order. And the frenzied efforts now under way to place thousands of unskilled CETA workers in an already-depressed job market are symptomatic of the anxious mood in Baltimore, as city officials prepare to wean themselves from the large portions of federal aid that nourished the city for years.

Today 13 mayors from across the country will tour projects in the city that would be crippled by the budget cuts before returning to Washington to meet with House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), in protest. But as they know from their own cities, CETA is already a lost cause.

Some regional Labor Department officials say they are under pressure to paint an optimistic picture of job searches such as the one under way in Baltimore, thereby proving the long-standing contention of the program's critics -- that CETA unnecessarily padded public payrolls with workers who could have found their own jobs if forced to do so.

But while even some civil rights leaders attacked the CETA program in its heyday as a dead end for those it enrolled, the men in Greene's class said they look back on it as the only thing that kept them off the welfare rolls.

"The only way I could get a job was to go through them programs and get mem a work record or a skill," said Fernandas Williams, 26, who spent 13 months cleaning city streets and vacant lots as a CETA worker. "As long as you work, you're moving up. Now there ain't nothing to look forward to."

While Greene and others work to ease the reentry of the CETA thousands into Baltimore's clogged job market, Mayor William Donald Schaefer is stalking the halls of the U.S. Capitol, pleading with one congressional committee after another to reject proposed federal cuts in a wide range of urban programs. Just as he touted Baltimore in more prosperous days as a model of the local-federal partnership, he now points to his city as a showcase of all that is wrong with the proposed budget cuts.

"All I ask some of you to do is to come down the road 30 miles to a little place called Baltimore and see what you have done" with federal funds, he said recently to a House Banking Committee panel studying economic stabilization. Unlike other mayors, who remained seated in conventional fashion while testifying before the committee, Schaefer jumped to his feet when his turn came and launched into a spirited, largely impromptu presentation -- complete with multicolored charts and graphs -- showing how the proposed cuts will hurt Baltimore.

"I don't mean to detract from the dignity of this chamber," he told the panel, growing more and more agitated as he detailed the anticipated cuts. "But I get a little nervous when I sit, especially when I'm talking about cities." From there, he detailed tens of millions of dollars of anticipated losses in programs that helped redevelop the city's old inner harbor, attract and keep industry, renovate abandoned housing, provide legal services for the poor and more. And then there were the 3,000 workers from the Comprehensive Employment and Training Act program who, he feared, had no place to go.

"You're not going to be able to take people and say: 'If the city goes down the drain, you will just evaporate,'" Schaefer said. "Because it just doesn't happen that way. They will still be there."

In the case of CETA, his aides noted, federal officials are eliminating the public service jobs, while retaining other CETA programs that train unskilled workers for jobs in private firms. It is more efficient, they argue, to move the poor toward private rather than public payrolls. However, there is no proposed increase in training funds to assist those being laid off. Baltimore officials contend they will fall between the cracks; Labor Department officials say they believe private companies can absorb them, and have enlisted business groups around the country to help out.

Schaefer concedes that he has little hope of winning the budget battle, but he has nonetheless attracted considerable attention on Capitol Hill with his unorthodox style and his impressive run-down of how federal aid has helped Baltimore. "I want to congratulate you," Rep. Stewart B. McKinney (R-Conn.), commented when Schaefer rested his case before the Banking subcommittee. "I don't think there's a federal program you haven't used."

The U.S. Conference of Mayors was apparently so taken with the presentation that it organized today's bus trip so that some of its members could see things for themselves.

As Schaefer talks about his city, he speaks with desperation. It is not just the Reagan cuts. It is also the Reagan tax relief proposal, which studies show will benefit the rich over the poor, meaning an extra burden for Baltimore's mostly middle- and lower-income population. And it is the 1980 census, which shows Baltimore losing more than 10 percent of its 1970 population -- down to 784,554 -- meaning lost clout in the state legislature after districts are redrawn to reflect shifting populations. That could translate into a loss of valued state aid, on top of the federal cuts, since the legislature decides how millions of dollars are allocated among governments.

But these consequences are months or years away. For now, the battle is concentrated in T. C. Green's classroom and others like it.

"Okay, how many of you don't have cars?" she calls out.She singles out a laid-off street cleaner -- one of the seven men who raised their hands -- and, playing the role of job interviewer, asks how he plans to get to and from work.

"Bus," he mutters, almost inaudibly.

"Naaaw, man. No way!" she says, reaching her large hands out toward him, prompting him to sit bolt upright in his desk. "You gotta use every answer to raise yourself up in that man's [the employer's] eyes. Two-year-olds can say 'bus.' Here's what you say: 'Pub-lic trans-por-ta-tion.'" She draws herself up tall as she slowly and firmly enunciates each syllable.

Each class leaves with this directive from Greene, an implicit acknowledgment that there are far more jobless Baltimoreans than there are jobs: "Now when you walk out of this room and into a job, I want you to look back over your shoulder and see the other people in this room who need a job. And wherever you are, if you see any openings on your job, don't forget these people. Call them and help them."

During a break in one of the classes, she noted wryly that she, too, is being paid through the CETA public jobs program. "And," she said with a half-laugh, "you know who loses her job when number 3,000 walks out my door, don't you?"