Los Angeles ? Matt Leinart’s first pass in a college game didn’t come until this year. He’s proved to be a fast learner.

Halfway through his first season as a starter for Southern California, Leinart quietly and efficiently is filling a huge void.

He has thrown for four more touchdowns than Heisman winner Carson Palmer had at this time last year, and his passing efficiency rating is more than 20 points higher.

“As the season’s progressed, I’ve felt way more comfortable taking grasp of the offense. We just want to keep this momentum going each week,” he said.

A year ago, USC was 4-2 and ranked 19th before Palmer and the Trojans won eight consecutive games, capped by a 38-17 Orange Bowl victory over Iowa.

This season, the fifth-ranked Trojans are 5-1, with the loss a 34-31 triple-overtime defeat at California on Sept. 27.

Leinart has thrown for 1,473 yards, with 13 touchdowns and seven interceptions — three at Cal. His passing efficiency rating is 146.9. Palmer had passed for 1,633 yards through six games last year, with nine touchdowns, six interceptions and a 124.6 rating.

“He’s only played six games. It’s scary to think about how good he can be,” receiver Keary Colbert said.

Notre Dame coach Tyrone Willingham, whose Irish play host to the Trojans today, also was impressed with Leinart.

“He’s very talented, and he had an opportunity to kind of see a very good quarterback perform — probably even better than that — in Palmer. He just had a fantastic year,” said Willingham, who watched Palmer throw for four touchdowns in the Trojans’ 44-13 win over Notre Dame last year.

“I think there’s also some learning that takes place when you’re that second guy just sitting and you’re watching and you’re learning from someone who is pretty good. But he has done an excellent job of stepping in, not being intimidated by their program or by the fact that he is stepping in and replacing Carson Palmer.”

Leinart also believes he profited from watching Palmer, both on and off the field. Palmer drew criticism when the Trojans struggled earlier in his career.

“I learned a lot about football, but I think mostly what I took from him was how he dealt with things, with adversity and success, how he carried himself,” Leinart said. “He had a lot of adversity, and turned it around. He took all the criticism and didn’t let it bother him, then in his senior season, he showed everybody.”

Leinart has played through nagging injuries this fall and is still limping slightly on a sprained ankle hurt Oct. 4 at Arizona State. He went out in the second quarter, but came back to help USC score 27 consecutive points in the second half of a 37-17 victory.

“I would have to have had a broken leg not to go back out there, and even then I probably would have tried,” said Leinart, a 6-foot-5, 220-pounder.

Colbert appreciated the quarterback’s grit.

“He showed a lot of courage and a lot of heart to come back out to play. The second half of that game, most people might not have. He’s out there hobbling around, hobbling into the huddle. It was a great thing,” Colbert said.

Last weekend against Stanford, Leinart finished 18-of-27 for 260 yards and threw three TD passes in a 44-21 victory.

“I think everything he’s done has made a good impression,” coach Pete Carroll said. “He has shown his toughness on a couple of different occasions, especially coming back in the Arizona State game. Then he played so well last week.

“He’s making a statement that he wants to be the quarterback here and be the leader.”

Leinart may face some competition if he stumbles. John David Booty, who skipped his senior year of high school to come to USC, already has vaulted to No. 2 on the depth chart.