Leaders of four conservative organizations, two of whom support Rep. Jack Kemp (R-N.Y.) for president in 1988, have sent Vice President Bush a letter encouraging him "to do whatever you can to gain the support of those House Republicans who have been reluctant in the past to support aid to the freedom fighters of Nicaragua."

The way to do this, they suggest, is to start at home. The letter points out that nine House members on the steering committee of Bush's political action committee, Fund for America's Future, "have in the past been unwilling to support aid to the contras." Bush is urged to "make a special effort to contact those individual members and solicit their support."

For Bush's "convenience," the letter included a list: Reps. Jim Kolbe (Ariz.), Nancy L. Johnson (Conn.), Stewart B. McKinney (Conn.), John G. Rowland (Conn.), Larry J. Hopkins (Ky.), Judd Gregg (N.H.), Hamilton Fish Jr. (N.Y.), Benjamin A. Gilman (N.Y.) and Frank Horton (N.Y.).

Those who wrote to Bush are: Robert C. Heckman of the Fund for a Conservative Majority, F. Andrew Messing of the National Defense Council, Michael Thompson of the Council for National Defense and Gary Jarmin of the Christian Voice Moral Government Fund. Heckman and Jarmin are Kemp supporters.