Goldman Sachs (GS), one of the few major U.S. investing firms that wasn’t covering Apple (AAPL), resumed coverage Sunday with a price target of $430.

The stock reacted immediately when trading began Monday, quickly setting an all-time intraday high of $325.06 as 1.4 million shares changed hands at the opening bell. It gave up some of its gains in late afternoon trading, but closed at 321.67, a new record.

In his note, Goldman’s new Apple specialist Bill Shope — formerly of Credit Suisse — dismissed concerns other analysts had expressed about weakening profit margins. “Indeed,” he wrote, “we believe Apple’s margins have already bottomed, and we expect the company to resume its leverage-driven upside in coming quarters.”

His note began:

“We believe Apple’s platform-centric business model is the secret sauce that has enabled it to quickly capture market share in new computing segments while simultaneously enjoying considerable margin leverage. Furthermore, we believe significant growth and profit opportunities for this platform still lie ahead. As a result, we expect revenue and earnings expectations to continue to trend upward, and we view the shares as attractive at current levels.”

[Follow Philip Elmer-DeWitt on Twitter @philiped]