A federal district judge in Texas ruled yesterday in favor of a plan by bankrupt Braniff Airways to sell or lease many of its planes and other assets to PSA Inc., a California airline that plans to open a major new operation centered at the Dallas-Fort Worth airport.

The ruling by U.S. District Judge Eldon Mahon in Fort Worth upheld a decision by the federal bankruptcy court there and included the requirement that the Federal Aviation Administration give PSA's new Texas Division the takeoff and landing rights once held by Braniff.

The FAA and many airlines--some of which now are using those landing rights, called slots--had vigorously opposed that section of the bankruptcy court ruling.

Attorneys for both American and Continental airlines said last night they would immediately appeal Mahon's decision to the Fifth Circuit Court of Appeals.

Braniff and PSA had indicated earlier that they would go forward with their plans on March 1 if there is no stay of the decision.

The judge's ruling was the second victory in the same day for PSA's Texas Division plan. Earlier, the Civil Aeronautics Board in Washington approved the joint operating plan and said there is no evidence that competition would be substantially harmed. In fact, the board said, "It is possible competition will be enhanced."

Since Braniff ceased flying and filed for bankruptcy last May, American Airlines has dominated the Dallas-Fort Worth market. An American spokesman says it is fighting the ruling on the grounds that Braniff owes it $8.7 million and "we do not think it is proper to give that to PSA."

The bankruptcy judge had held that Braniff's unsecured creditors would recover a larger portion of their losses if the PSA proposal were approved than they would if its assets simply were liquidated.

PSA said it would hire as many as 2,000 of Braniff's former 8,000 employes and would extend service from Dallas-Fort Worth to 15 other airports, including Washington National. The Texas Division would interconnect with PSA's network at six western cities.

Braniff held 411 slots nationwide when it declared bankruptcy. About 350 of those slots have been reallocated by the FAA to other airlines, and they are not anxious to give them up. If PSA's new Texas Division is to find room within the air traffic system to fly, either the system will have to be expanded at a time when it is recovering from the 1981 controllers' strike, or somebody else will have to relinquish slots.

The bankruptcy court had held that the slots were property and part of the Braniff estate. Mahon's ruling, if it stands, thus creates substantial logistical problems for the FAA, which had contended that it controlled the slots.

The CAB said in its decision yesterday that it will not address the slot issue, because that question "should be decided in a different forum."