At some of the country’s top firms, younger lawyers will foot the bill for deluxe pension plans that could drag down their own earnings for years to come. These pensions are largely unfunded: there is no money saved to pay retirees. Instead, most law firms with such plans pay the benefits as they go, using a portion of their current profits. Partners at some elite firms are often entitled to between 20% to 30% of their peak pay after retirement — in many cases, for life, according to partners and law firm consultants. For the most profitable firms, that could mean payments of $400,000 to $600,000 a year per retired lawyer. In its own way, the future liabilities for some top law firms mirror similar problems across the U.S. Benefits promised in more stable economic times seem increasingly unsustainable today. From General Motors Co. and AT&T Inc. to cash-strapped local governments employing public workers, pension liability is becoming a growing concern as the retiree pool swells.