Lawrence W. (Slippery) Jackson, who was paroled in December 1979 after serving almost 10 years in prison on narcotics charges, pleaded guilty yesterday in federal court in Baltimore to conspiracy and heroin distribution.

Jackson, 45, who has been described by law enforcement sources as a major heroin wholesaler in Washington, faces up to 30 years in prison on the two charges, although the prosecution has agreed to recommend to the court that he be ordered to serve 25 years.

In addition, Jackson could be required to serve another 21 years in so-called backup time, which includes 16 years that remained on his original drug conviction at the time he was paroled and five years on an earlier counterfeiting conviction.

Assistant U.S. Attorney Price O. Gielen said in court yesterday that in exchange for Jackson's guilty pleas, the prosecution will drop five additional charges against him, each of which carried a maximum penalty of 15 years in jail. Jackson is expected to be sentenced in Baltimore within the next 45 days.

Gielen also told U.S. District Judge Edward S. Northrop yesterday that Jackson also has agreed to forfeit $7,400, allegedly cash proceeds from drug sales that were taken from the trunk of his black limousine by law enforcement officials at the time of his arrest. Gielen said Jackson has agreed to turn over the money even though a court ruled that police acted illegally when they seized the money from the car.