WASHINGTON (Reuters) - Republicans in the House of Representatives hope to offer President-elect Donald Trump an alternate plan to his proposed U.S.-Mexico border wall, a first test by lawmakers from his own party of one of his key campaign promises. Just a day after Trump’s stunning election victory over Democrat Hillary Clinton, congressional aides told Reuters the lawmakers wanted to meet with Trump’s advisers to discuss a less costly option to his “big, beautiful, powerful wall.” The plan would involve more border fencing and additional border staffing with federal agents, many of whom belong to labor unions that supported Trump’s candidacy, the aides said. Double layers of fencing would be extended along parts of the roughly 2,000-mile (3,200-km) border, rather than constructing a brick-and-mortar wall, according to the proposal. A House Republican aide and a Department of Homeland Security official said a wall was not realistic because it would block visibility for border agents and cut through rugged terrain, as well as bodies of water and private land. The House aide said House Republicans working on the alternative plan were waiting for Trump’s transition team to be put in place before setting a date for the meeting. A spokesman for Trump did not respond to a request for comment on the lawmakers’ proposal or their desired meeting.  Mexico said on Wednesday that it would not pay for a border wall, as Trump has pledged. Immigration was a central feature of the Trump campaign, focusing on concerns among some voters about illegal immigrants and perceptions they take jobs and pose security risks.  Before the Republican convention in July, party platform committee members successfully petitioned delegates to add language about the proposed wall to the platform statement.  But U.S. Republican Representative Michael McCaul, chairman of the House Homeland Security Committee, has called a wall along the entire border a “knee-jerk” reaction and has not mentioned the idea in legislation on Capitol Hill.  If Congress stands up to Trump, his wall may end up being a fence extension, said Steve Legomsky, professor emeritus and immigration law expert at Washington University School of Law. “Congress won’t fund the kind of wall Trump promised, and Mexico won’t pay for it. But to save face, President Trump and congressional leaders will likely agree to a modest extension of the existing border fence,” Legomsky predicted. Senate Majority Leader Mitch McConnell told reporters on Wednesday that border security was an important agenda item that he wanted to achieve “in whatever way is the most effective.” The National Border Patrol Council, a union representing border agents, said the agency had already had a difficult time meeting hiring goals mandated by Congress. 