A Christmas Eve court ruling that the government acted unconstitutionally by skirting parliamentary opposition to the budget stems from dissension within the legislature's majority, according to political observers here.

The ruling reflected guerrilla warfare between the followers of President Valery Giscard d'Estaing and Prime Minister Raymond Barre on one side and the Gaullists on the other, they said.

The Gaullists had demanded a $500 million cut in the budget. Barre got around them by holding the budgetary debate without the constitutionally required vote beforehand on total government revenues to be collected for 1980.

National Assembly President Jacques Chaban-Delmas, a Gaullist, joined the opposition Socialist Party in requesting that the nine-member Constitutional Council rule on the constitutionality of the procedure. The council, which has generally rubber-stamped government action, is chaired by Roger Frey, another veteran Gaullist.

Bare is expected to call an emergency special session of parliament and have the budget passed without difficulty by challenging the Gaullists to bring down his government by voting for a motion of no confidence.

If there is no majority for such a motion, the legisltion in question is considered automatically adopted. Barre used this extraordinary procedure four times in the past session of parliament, forcing the Gaullists to demonstrate that their opposition is only verbal.