Insurers point to several reasons that premiums will rise. They will soon be required to offer more-comprehensive coverage than many currently provide. Also, their costs will increase because they will be barred from rejecting the sick, and they will no longer be allowed to charge older customers sharply higher premiums than younger ones…

The insurers’ public relations blitz is being propelled by a growing cast of executives, lobbyists, conservative activists and state health officials. They increasingly use the same catchphrase — “rate shock” — to warn about the potential for price surges.

Aetna chief executive Mark T. Bertolini invoked the term at his company’s recent annual investor conference, cautioning that premiums for plans sold to individuals could rise as much as 50 percent on average and could more than double for particular groups such as the young and healthy.

The danger of rate shock has also become the favored weapon of conservative opponents of the law, repeated in a drumbeat of op-eds and policy papers in recent weeks.