Justice Department officials predicted yesterday that there will be few problems in the implementation of new federal sentencing guidelines and denied assertions that prosecutors, defense attorneys and judges are not prepared for the new system.

"We are ready for this. We are certain this is going to work," Associate Attorney General Stephen S. Trott said during a news conference. The guidelines, which are mandatory, became effective Sunday for crimes committed that day or later.

Drafted during the last 18 months by a commission that was appointed pursuant to the 1984 Comprehensive Crime Control Act, the guidelines employ a mathematical formula to determine minimum and maximum sentences, based on the actual crime committed.

The new system eliminates parole and reduces the amount of "good time" credit a federal prisoner may earn, resulting in what Trott described as "real-time sentencing." He said the guidelines will eliminate the "vastly different sentences" that are now being imposed for similar crimes, and mean a "greater certainty of incarceration" for persons convicted of white-collar crimes and public corruption.

Trott predicted that the guidelines will fuel a "real revolution" that will "alter the criminal justice system considerably."

But he brushed aside complaints from prosecutors, judges, defense attorneys and the American Bar Association that the system is ill-prepared for the change, saying that the "best way" for prosecutors to learn the new system is on-the-job experience.

The final guidelines, with explanatory commentary, were distributed to judges and prosecutors only last week and copies of that publication are not yet available at government bookstores for purchase by defense attorneys and others.

Few training programs have been held for defense attorneys and training for prosecutors and probation officials is still getting off the ground.

Assistant Attorney General William Weld, who heads the criminal division, said representatives of each U.S. attorney's office and each probation office have been trained and that the final guidelines, without the explanatory commentary, have been available since April or May.

Weld said that persons convicted of violent crimes and drug offenses will receive "substantially greater" sentences under the guidelines.

He said that because of the "new guidelines and other statutory changes" in recent years, including the imposition of mandatory minimum sentences for some drug offenses, a "big impact" on the federal prison population is expected during the next decade.

The sentencing commission has predicted that the number of federal inmates could rise to 125,000 by 1997, and the Justice Department has estimated the population could increase to 76,000. There currently are 45,953 federal inmates.