WASHINGTON (AP) - Senators in a bipartisan group crafting a comprehensive immigration bill said Tuesday they're not sure whether they can meet a self-imposed March deadline but they're optimistic about a deal soon. The lawmakers in the "Gang of Eight" have been meeting several times a week to write sweeping legislation that would strengthen the U.S.-Mexico border, improve legal immigration, crack down on employers who hire illegal immigrants and provide an eventual pathway to citizenship for the 11 million illegal immigrants already in the U.S. When they unveiled legislative principles in January, the senators announced they hoped to release a bill sometime in March. Now, several senators - including John McCain, Lindsey Graham and Marco Rubio - say they're not sure if they'll meet the goal. But lawmakers downplayed the significance of a short delay. "I don't know about timeframe, I'd rather do it right than do it fast," Rubio said. But I think we're making good progress. Congress is on recess the last week of March and first week of April. The senators are likely to release their legislation soon after they return from the recess, and there would likely be a vote in the Judiciary Committee soon thereafter. The legislation is certain to be controversial and may spark passionate opposition from lawmakers' constituents at town halls and elsewhere. Such opposition helped sink the last congressional attempt at overhauling immigration laws, in 2007. So even if it were finished in time, Graham said it wasn't a good idea to release the bill before a two-week recess. "You don't want to leave it hanging out for two weeks to get shot up," he said. A number of thorny details remain unresolved. Lawmakers said one of the toughest is figuring out the design of a temporary worker program that would govern how future low-skilled workers can come to the U.S. Graham and Sen. Charles Schumer, D-N.Y., had asked the Chamber of Commerce and AFL-CIO to try to work together to resolve the issue, but after agreeing last month on broad principles, the two sides have not reached final resolution. Senators have been intervening to try to work out the details and AFL-CIO President Richard Trumka and Chamber of Commerce President Tom Donohue both were on Capitol Hill Tuesday for meetings.