Blacks in Government (BIG), an organization of black federal, state and local government employes, yesterday announced it would begin a special effort to monitor the treatment of blacks in future federal reductions in force.

The group also released copies of recent correspondence with President Reagan in which the president denied BIG's assertion that black federal workers have been targeted in government layoffs or downgradings.

"I would not tolerate such a practice, and I would very much like to know of any situation you may be aware of where blacks or other minorities are being targeted in either a RIF procedure or forced retirement," Reagan wrote BIG president Mildred Goodman. His letter was in response to her contention at a BIG conference here in September that blacks are bearing a disproportionate share of the RIFs.

Replying to Reagan's letter, Goodman wrote the president in October, citing three instances in which she said blacks had been targeted. She asked him to appoint a special task force to review "the disproportionate adverse impact on minorities" agency by agency. She said that the group knew of many cases of RIF discrimination but that the individuals involved were reluctant to step forward for fear of reprisals.

"We're taking the position that the president simply has not been informed and that it's up to us to give him the kind of information he would not get otherwise," Goodman said yesterday.

BIG named William Johnson, former director of public affairs for the Federal Highway Administration, to head the monitoring effort, which will be called Agency Watch. The group hopes to collect RIF statistics, as well as information on hiring practices, turnover rates, quality and quantity of training opportunities, awards and promotion rates.

Pointing to a survey by the Federal Government Service Task Force, Goodman said minorities comprised 39.2 percent of the 5,321 employes separated by RIFs during the first two quarters of fiscal 1982. Minorities made up 39.1 percent of the 2,327 employes downgraded during that same period. Yet, Goodman noted, minorities constituted only 21.9 percent of the government's total work force then.

While acknowledging yesterday that blacks often are RIFfed because they have little seniority in an agency, Goodman said federal managers also are able to "manipulate" a RIF because they know about it well in advance. They can thus protect some employes from layoffs or being downgraded, she said, by giving them "outstanding" performance evaluations that increase their chances of retention.

She said the situation was less an attempt to "get rid of black employes" than a case of "I'm going to take care of my white buddies."