www.nytimes.com Many of the country’s largest casinos, long opposed to gambling games like poker on the Internet, are now having second thoughts. Although online gambling is popular with millions of Americans, it is illegal in the United States, and the casino industry has considered it a threat. But a trade group that represents major casinos like Harrah’s Entertainment, MGM Resorts and Wynn Resorts is working on a proposal that would ask Congress to legalize at least some form of online gambling, the group’s chief executive said. The group, the American Gaming Association, issued a statement in the spring suggesting that online gambling could be properly regulated — the first public indication that its hard-line stance was softening. The chief executive, Frank J. Fahrenkopf Jr., said in an interview by phone that the association had not settled on the details of its proposed legislation, including how the proceeds from Internet gambling would be taxed. “We have been working on something,” he said, “and continue to work on it.” Gambling specialists said it was likely that any casino-supported legalization would be limited to Internet poker because it was considered the least threatening to brick-and-mortar casinos. Internet poker already had the backing of some in the casino industry, and was seen as a new and lucrative source of revenue for the casino companies. Congress has been weighing a bill by Representative Barney Frank, Democrat of Massachusetts, that would …