In what may be the first substantial victory for Vice President Bush in his continuing party battles with Marion G. (Pat) Robertson, the Louisiana Republican Party yesterday approved a delegation selection process backed by Bush supporters.

"We went to war," said Lanny Griffith, Bush's southern political director, "and we won." The Bush forces succeeded in rejecting by an 81-to-45 vote a delegate selection plan back by Robertson and Rep. Jack Kemp (R-N.Y.).

The Robertson-Kemp forces wanted to set up a system calling for the selection of delegates through a series of county, district and state-wide caucuses -- the kind of terrain in which Robertson supporters have excelled. Under the rejected plan, these delegates would have gone to the national convention if no candidate won more than 50 percent of the vote in Louisiana's March 8 primary.

Such a plan would have allowed Robertson to engage Bush in a caucus fight before the Super Tuesday primaries on March 8, with a strong possiblity of embarrassing Bush.

The GOP central committee meeting in Baton Rouge decided, however, to accept a plan that basically allocates all delegates on the basis of the outcome of the March 8 primary. Three delegates will be elected from each congressional district, with the winner of a plurality of the vote getting all three. In the central committee fight, Bush supporters said they were backed by members aligned with the campaign of Sen. Robert J. Dole (R-Kan.).