WASHINGTON — President Obama met with insurance industry executives at the White House on Friday to coordinate the introduction this fall of the insurance marketplaces at the heart of the national health care law, and to discuss so-called rate shock if the industry sharply raises premiums. "We're all in this together," Mr. Obama told the executives, according to people with knowledge of the meeting, who spoke on the condition that they not be identified discussing it. Government and industry, which battled while forging the law, are now "joined at the hip," the president said at one point. "We're going to make it work."