Dennis Murphy celebrated his 35th birthday in grand style last night by winning the Second Ringmaster Challenge Trophy for a second consecutive year, riding the Gulf States Paper Corp.'s 12-year-old chestnut gelding Tuscaloosa.

Murphy was the ninth rider in a field of 28 to enter the ring for the class, which was scored as faults converted into seconds. Four seconds were added to the rider's score for each pole knocked down.

Murphy whipped Tuscaloosa around a course of 11 jumps in a blistering time of 37.17 seconds and then sat back to watch the rest of the riders try to beat his time.

Fourteen others went into the ring before Armand Leone, 22, on Sombre came close at 38.76, good enough for a second place finish.

Murphy, who claims Tuscaloosa, Ala., as home, said of his mount, "I think he's a better horse than I am a rider. He is very experienced in this type of competition. He is aggressive and attacks the course. You just have to show him where the jumps are."

Murphy has represented the United States in international competition on many occasions, including the 1975 Pan American games, where he was a member of the gold medal team. He said Tuscaloosa was just coming back after a three month layoff due to an injury.

"He was hurt last summer. He got a splint on his leg and had to be laid up. Tonight was his first class since being out to pasture."

The course was designed with a number of options, such as a two-part jump at the far end of the ring with the inside part lower. Murphy felt that this played an important part in his victory. "He knows when he gets to the end of the ring that it's time to come back. He anticipates the flow of the course."