D.C. Democratic mayoral candidate Sterling Tucker, stepping up his attack on Mayor Walter E. Washington as they head toward next Tuesday's primary in a virtual dead heat, charged on Labor Day yesterday that "of all the major challenges faced" by the mayor, "his most miserable failure is on the jobs issue."

City Council Chairman Tucker said the mayor had not adequately enforced the law requiring that 25 percent of city contracts go to minority firms, that he had failed to fully use federal funds to create private jobs and had provided "irrelevant and inadequate" job training and no couning for school youths seeking work.

The present mayor's unforgivable sin is in not - in the face of the spreading unemployment emergency - having fashioned and vigorously implemented a comprehensive job-creation program. He appears to be mesmerized by the fiction that the national government, a force beyond his control, is the sole employer," Tucker said.

"Like a biblical farmer awaiting needed rains," Tucker said, "he fatalistically hopes for an upturn in the local job market. The present mayor, in summery, was leaning on his broom when he should have gotten on the stick to create employment for the people."

Tucker attacked the mayor's job effort at a press conference he called to release his sixth campaign position paper on D.C. issues. But aside from specifically talking about the city's high unemployment rate for youths and other job statistics, Tucker's statement once again tried to sharpen the undecided voter's focus on differences between himself and the mayor.

A spokeswoman for the Washington campaign said yesterday there would be no comment "at this time" on Tucker's allegations.

A Washington Post poll of 762 registered Democrats last week showed Tucker leading Washington, but only narrowly, by 31.4 percent to 30.8 percent, with the third major candidate in the race, City Council member Marion Barry, getting 23.5 percent.

Undecided voters "will now see that Marion Barry is not a viable candidate, that he will not win," Tucker said. He and his advisers are hoping that they can persuade enough voters, including some current Barry supporters, that they should now vote for Tucker if they want to insure that Walter Washington is not mayor for another four years.

One source close to the Tucker campaign said its polling operation had shown that many voters in the city generally "feel good" about the resurgence of the city in recent times, including congressional passage of the constitutional amendment to give D.C. voting representation in the Senate and House. Some of that good feeling has been transformed into additional voter support for the mayor, the source said.

But Tucker said yesterday that he believes the mayor "has peaked. I think he's succeeded in consolidating his base."

In his statement on jobs, Tucker particularly faulted the mayor for losing D.C. jobs to the suburbs.

"Mayoral malingering has caused the District to come in dead last in the regional race for jobs,"Tucker said.

He said that while the metropolitan area as a whole had 65,000 new jobs in the 1965-1977 period, the District "suffered the staggering decline of 24,000 jobs." In the last seven years, Tucker said, the area increased its work force by 17.3 percent, "compared to a measly 1.8 percent for the District." He said the city had lost 4.7 percent of its private jobs and only showed an overall increase through higher government employment.

He said the District's youth unemployment rate is especially high, 44.4 percent, but that some estimates have placed the figure even higher because many young people have simply quit looking for work and thus are not reflected in the unemployment statistics.

"The city booms for whom?" Tucker asked. "Not for high school students."

Tucker said that his record of securing jobs as executive director of the Washington Urban League from 1956 to 1974 shows "there are few city leaders - certainly none in this mayoral race - who come close to Sterling Tucker in experience and accomplishment on the challenge of creating work for the unemployed."

He said that if he is elected mayor he would appont an employment coordinator in his office to oversea the creation of more jobs, actively recruit more "nonpolluting, labor-intensive enterprises" in direct competition with the suburbs, make greater use of the federal Comprehensive Employment and Training Act program to create more jobs and actively enforce minority hiring plans in the city.

"In sum, the Tucker administration will create a jobs-now mentality he said.