The traditionally liberal District of Columbia City Council began to consider yesterday a raft of no-nonsense, anticrime proposals, but quickly found the city's two top prosecutors and the American Civil Liberties Union in an unlikely alliance opposing mandatory sentences for criminals.

On the one side, with conservative calls for five sentences for specific crimes, were such liberal activists as City Council members Betty Anne Kane (D-At-Large) and John Ray (D-At-Large). Opposing them were U.S. Attorney Charles F. C. Ruff, a former Watergate prosecutor, and D.C. Corporation Counsel Judith W. Rogers, whose office prosecutes the rising number of crimes committed by juveniles in the District. p

The mandatory sentencing proposal was just one of a package of tough measures that would, among other things, ban the sale of drug paraphernalia, lengthen the time in which charges could be brought against some suspects and make it easier for prosecutors to hold suspects in jail pending their trials.

In the past, such stiff anticrime bills would have been considered too conservative, especially by a City Council composed of liberal Democrats, many of them former civil rights activists. But the city's soaring crime rate and heightened community fears have made it politically acceptable to champion anticrime legislation.

The use of mandatory sentences for certain crimes has become the key issue in the council's debate. In hearings yesterday, Ruff and Rogers, as well as officials from the D.C. Parole Board, the city's corrections department and the ACLU, all told council members that the proposed mandatory sentencing bills would not deter crime. Instead, they said, such penalties would in many cases tie the hands of prosecutors who can now obtain criminal convictions through plea-bargaining arrangements.

"I oppose the institution of mandatory minimums," Ruff said. "Picture the case of your mother or sister who is charged with an offense. Don't you want the prosecutor to have the discretion to say your sister is a special person, and hers is a one-time offense?"

Rogers, the city's chief legal officer, said she agreed with Ruff's remarks, and added that mandatory sentences would further burden the city's overcrowded prisons. She said that corrections department officials are also opposed to mandatory sentences, since prisoners who receive mandatory penalties -- and thus have no chance of early release -- have no incentive to cooperate with prison rules.

ACLU Director Lesli A. Harris said that the current crime problem has nothing to do with the sentencing process, but with the fact that "criminals are simply not being caught."

The debate over mandatory sentences, especially for gun-related crimes, is being held nationally, pitting politicians who see mandatory sentences as a response to community fears against law enforcement professionals who see those same penalties as unduly burdensome and essentially worthless as a way to stem crime.

The debate is likely to emerge further as the Reagan administration attempts to form a national anticrime policy and guidelines for the Justice Department. In position papers on crime during the 1980 campaign, then-candidate Ronald Reagan voiced strong support for mandatory penalties "for commission of armed felonies, rather than gun registration, as the most effective means to deter crimes" in which a gun is used.

However, the Justice Department has "always been opposed generally to a lengthy minimum sentence," spokesman John Russell said. He added that the new administration has yet to adopt official guidelines for sentences.

Kane's bill would require a five-year mandatory sentence for the use of a dangerous weapon in a crime, while Ray's bill, which covers only firearms, sets a mandatory two-year sentence for a second gun offense.

"Some of the opposition I hear from professionals to mandatory sentencing is that it will mess up the system and keep the system from working," Kane told Ruff. "What I hear from the community is that the system isn't working now."

Ray, who later called Ruff's remarks on mandatory sentences "hogwash," said he favored the fixed sentences because of the discrepancy between penalties imposed on poor defendants and wealthier, middle-class defendants who can afford better lawyers. Under current law, which leaves sentencing discretion to judges in most cases, Ray said, "Those who are poor, those who are black, are the ones who end up with the tough sentences."

"By and large," Ruff replied, "I think there is no evidence -- none -- that there is any discrimination in sentencing between the black man and the white man."

The prosecutor said that he favors loosening prosecutors' hands by allowing them to seek to have more suspects kept in jail before their trials.

The hearings on the proposals continue today.