Democratic mayoral candidate Patricia Roberts Harris, characterizing herself as a better administrator than politician, said yesterday that if elected, she would improve services of a city bureaucracy she considers second rate and better protect the interests of the poor.

The 58-year-old former ambassador and Carter administration cabinet member said she would dramatically step up the city's job placement services, providing free transportation for some city residents applying for jobs in the suburbs and improving public commuting systems for those already working there.

She said she would reduce what she termed a shamefully high rate of infant mortality and tuberculosis in the city, and would favor compulsory prekindergarten education, similar to successful national efforts such as Head Start, for all 3- and 4-year-old children in Washington.

Harris, the leading challenger to incumbent Marion Barry in the Sept. 14 primary, said that in order to win the nomination she must overcome the notion that the District of Columbia, with a 70 percent black population, can get along with an inefficient and wasteful government.

"I know that I can improve this city's performance in dealing with every aspect of government responsibility," Harris said in an interview with reporters, editors and editorial writers of The Washington Post. "And despite the [recent Post] editorial that admonished us not to assume that the District of Columbia is doing so badly, it's important that a 70 percent [black] city have a sense of accomplishment and if possible a sense of leadership in solving problems at the local level."

Harris expressed frustration with those who seemed willing to disregard what she termed the many mistakes that Barry has made since taking office Jan. 2, 1979, or who seem swayed, she said, by favors he has been able to bestow as the incumbent.

"There is an interesting failure to look at what has not happened over the last 3 1/2 years," Harris said. "It is almost as if people have suspended their memory over what happened . . . and are now checking who had the biggest party, who got the largest number of employes of the District government at a party, and not on what have we failed to do over the last 3 1/2 years and who has made proposals for doing something in the next four."

Harris, who was secretary of the federal departments of Housing and Urban Development from 1977-79 and Health and Human Services from 1979-80, said that over the years Barry has done a far better job than she of developing a network of political supporters -- primarily because she has tried not to mix government work with politics.

"The use of the public business for private gain of a political nature is something I declined to do with my federal job or in the private sector," Harris said. "I do not convert what is public business into a private benefit. And that's what everybody cynically thinks is political."

Wearing a beige suit and a white blouse, Harris was relaxed yet methodical when responding to questions. She was accompanied by her campaign coordinator, Sharon Pratt Dixon, and by real estate executive Flaxie M. Pinkett, Harris' longtime friend and campaign finance committee cochairman.

During the wide-ranging 90-minute interview, Harris painted a picture of a D.C. government bureaucracy plagued by unimaginative and inept leadership and missed opportunities.

"This city is at the bottom of performance," she said, comparing it with other cities. "It would be bad under any circumstances, but for this to be another example of the failure of a disadvantaged minority that suddenly comes into authority, to me is unacceptable."

Harris listed as her top priorities reducing the city's unemployment rate, which was 11.3 percent in June; sparking economic development outside the downtown area; speeding up renovation of dilapidated public housing; improving financial planning; and better coordinating the efforts of local and federal law enforcement officials to combat crime.

She pledged that in her first term:

* D.C. residents would be assured of obtaining at least one-tenth of all new jobs that open up in the Washington metropolitan area, through aggressive job-placement activities by the Department of Employment Services (DES) and outside contractors. She said the DES currently ranks in the bottom third of the country in job placement and overall service.

* The worst of the city's public housing units, sheltering 1,200 families, would be completely renovated.

Barry claimed earlier this week that his administration spent more than $32 million and renovated more than 2,900 public-housing units. But Harris said yesterday that the city is sitting on about $40 million in renovation funds and that only 50 of the 2,900 units cited by Barry were fully renovated. The rest underwent repairs and improvements, such as installation of new windows or roofs, to bring them up to code.

"When somebody says to me, 'I have rehabiliated 2,000 to 3,000 public housing units, I simply say that it is not true," said Harris. "Fifty units -- 50 -- have been completed."

* She would further reduce the city's $309 million accumulated deficit -- partly by redefining what constitutes the deficit to no longer include nearly $211 million in city employes' accumulated vacation time. However, Harris said she would need federal legislation to accomplish that.

Harris repeatedly asserted that she was the only one of Barry's three Democratic challengers who has offered comprehensive proposals for improving services and encouraging economic development to expand the tax base and bring new jobs to the city.

However, City Council members John Ray and Charlene Drew Jarvis, the two other candidates, have each unveiled a series of proposals for improving city government. Jarvis, chairman of the council's housing and economic development committee, contends she introduced a bill to establish a city economic development corporation months before Harris came up with the idea.

But Harris said that her proposal for a semiprivate economic development corporation and a land bank of surplus city-owned land to retain businesses and to encourage commercial development in depressed areas such as New York Avenue NE is more comprehensive than Jarvis' plan.

"It's important that we have in place an institutiion that can bring together the now duplicated forces and operations [of city agencies] . . . so they can all have a focus about retaining what we have," Harris said. "There is a hemorrhage of business out of this city."

To combat what she has described as an alarming increase in the rate of serious crime, Harris would create a committee to coordinate efforts of police, prosecutors and the courts.

Harris said that Barry's efforts to combat drug trafficking with periodic police sweeps has been ineffective because few of the 5,000 or more arrests since last summer have resulted in convictions.

Harris, a lawyer, said she favors the use of plea bargaining in obtaining convictions for less serious crimes, as long as it is tied into reasonable sentencing, probation and counseling policies.

She also favors creating a program, administered by the Department of Human Services, to provide direct aid and services to victims of crimes. Harris insisted that the program, which would be operated out of district police stations, would not cost the city additional funds.

Harris said that many of her proposed intiatives would not add to the city's budget because she would achieve economies in other areas with management by objective techniques that she used as a cabinet secretary.

The only proposal that would require a significant increase in spending, she said, is her plan to require children to begin attending school at age 3 instead of 5, as is now the case. That plan, she said, largely designed to assist children from poor and socially disadvantaged families, would have to undergo intense community and professional review.

"I am convinced that urban school problems are largely problems of lack of socialization of poor children, so that when they come into the school system they find themselves behind their middle-class peers," Harris said.

"I believe we ought to bring children into the school system at age 3 -- require all children, middle-class children and poor children" to begin school then, she said.

"First of all," Harris said, "everybody starts equal; second, we learned from two programs stasrted in the 1960s [including Head Start] that programs started for early education of the poor do work."

She also said that as mayor she would attempt to provide leadership in the area of education and cooperate closely with the D.C. school board.

During the interview, Harris took credit for providing federal assistance for several major projects benefiting the District, including the Hechinger Mall in Northeast, the Capital Children's Museum in Northeast, the J.B. Johnson Center for the elderly and funding for renovations of the James Creek public housing project in Southeast.

As secretary of HUD, Harris helped develop what most considered a highly successful Urban Development Action Grant (UDAG) program, that provided federal funds to spur local commercial development, such as the Hechinger Mall and Baltimore's Harborplace. But only a relatively small amount of the funds came to the District.

Harris denied that she could have been more helpful to the District in getting a larger share of the UDAG grants and blamed D.C. officials for not being more aggressive in going after those funds.

"The one thing I insisted on with respect to the UDAG program, the thing that saved it in the Reagan administration, is that it be operated entirely as rules required," she said. "I did not cut corners politically. I did not make political deals for anybody."

"What I did for the District of Columbia, what I did for Knoxville, Tenn., when they did not bring in proposals that met the requirments of the program, we gave them technical assistance . . . We did it for the District. They couldn't even do what they were told."