WASHINGTON, Nov. 25--The Senate Banking Committee gave President Johnson's new administration its first congressional victory today, recommending against a proposal that might have blocked grain sales to the Soviets. At stake is the sale of some 150 million bushels of wheat to communist countries approved by the late President Kennedy.

By an s-7 margin the committee voted against a proposal by Sen. Kerl E. Mundt (R.S.D.), to ban use of government loans or financing guaranteeing that American sellers will be paid for the grain they ship to Iron Curtain countries. The committee vote first was announced as a 7-7 tie, but Sen. Harrison A. Williams (D.N.J.), sent his proxy to provide the margin against it.

The measure now goes back to the Senate for its consideration, possibly Tuesday or Wednesday, A speedy decision is needed since officials of the Export-Import Bank have agreed to delay action on wheat deals until the Senate acts on Mundt's bill. The bank has agreed to underwrite sales of $25 million of U.S. wheat to communist Hungary.