President Obama on Wednesday extended a modest package of benefits to the same-sex partners of federal employees, a move that will make them eligible for day care, travel and relocation allowances, employee assistance programs and, in some cases, enable them to inherit retirement benefits. But Mr. Obama lamented that federal law  the Defense of Marriage Act  prevents him from extending the full range of health and retirement benefits to federal employees. He called on Congress to pass legislation that would allow him to do so.