A Boston-based legal group asked the US Supreme Court Wednesday to review a Connecticut lawsuit challenging a key portion of a federal law that denies tax, health, and other benefits to same-sex married couples. A federal judge in Connecticut ruled last month that Section 3 of the 1996 Defense of Marriage Act is unconstitutional. The ruling came in the case of a widower and six married gay couples from Connecticut, New Hampshire, and Vermont, who sued after being denied federal benefits. The Defense of Marriage Act defines marriage as the legal union of one man and one woman. Section 3 of the law restricts federal marriage benefits to heterosexual married couples. Gay & Lesbian Advocates & Defenders, which is based in Boston, filed a petition Wednesday asking the Supreme Court to review the ruling. A congressional group and the Justice Department have asked the high court to review a ruling by a federal judge in Massachusetts striking down the same provision of the law in two separate lawsuits.