D.C. School Superintendent Vincent E. Reed took a liberal congressman "back to basics" yesterday -- disputing the member's view that students can only learn when they are not watched by police.

Reed at a hearing into urban problems, told Rep. Ronald V. Dellums (D-Calif.) that improved security in Washington's 200 school buildings is one of his unmet priorities. "Our schools are at the mercy of the thugs and hoodlums in this city . . . [with] kids and teachers shot and mauled," Reed declared.

When Dellums voiced doubt that a good education was possible with guards patrolling the hallways, Reed replied bluntly:

"I don't have time for that kind of rhetoric. . . . We've got to be realistic in cities. . . . We don't have anybody [in the schools] trained to deal with anybody who come in with a weapon."

As recently as Wednesday, Reed testified, an armed robbery took place in a Washington school. He provided no details, but D.C. police reported later that a man wearing a stocking mask and carrying a shotgun entered Eastern High School after summer classes were dismissed for the day and robbed a nurse, Evelyn Boston, of $10.

Last year, there were more than two dozen shootings and 1,000 robberies, assaults and thefts reported in school buildings.

Reed's testimony sounded the only discordant note in four days of House District Committee hearings conducted by Dellums, one of a group of liberals fighting budget cuts proposed by President Carter, claiming they will lead to more social disarray and despair.

More than a dozen previous witnesses, including Mayor Marion Barry on Wednesday, told Dellums what he wanted to hear.

But Reed, taking the witness chair yesterday, said "most of these sessions are a waste of time" if they only restate of the obvious.

Reed's main theme was that the city's school system is disoriented because it has had eight superintendents in the 12 years before his own appointment from the ranks in 1975.

With many of those problems now being solved, Reed said student achievement -- as measured by standardized test scores -- is on the upswing. But, coming back to Dellums' theme, he said this is now threatened by the city's financial crisis which is forcing the schools to lay off 1,333 of their 6,658 teachers.

Acknowledging that his comments might be viewed as self-serving, Reed said his efforts to improve education are frustrated by constant battles between school board members and the intrusion of some members in the process of school administration. He did not mention any names.

"Boards of education can't run school systems; it's the superintendent's responsibility," Reed declared. "I am doing what I can till they get six votes [of 11 on the board] to get me out of there . . . If we can take [most of] the politics out of education [and] put it back in the hands of the [superintendent] who is responsible, I think there is some hope."

Dellums asked Reed what the federal government could do to help the school system most. Reed replied that it could help pay for improved security.

Dellums, whose California district includes Berkeley and much of Oakland, has two children now enrolled in the D.C. public schools. Four years ago, Dellums' wife told an interviewer that one of them, a son then attending junior high, was so afraid of some students that he would not use the school's bathroom.

Reed said one major security problem is fire regulations that prohibit the schools from locking exit doors during school hours to keep out strangers and other outsiders. Some large schools have as many as 85 to 90 exit doors, Reed said.