(Adds European officials saying 21 days to comply with some requirements)
WASHINGTON/NEW YORK, June 28 (Reuters) - U.S. Homeland Security officials on Wednesday will unveil enhanced security measures for foreign flights arriving in the United States but not an immediate expansion of an in-cabin ban on laptops and other large electronic devices because they might carry bombs, sources briefed on the matter said.
The decision not to impose new restrictions on laptops is a boost to U.S. airlines, which have worried that an expansion of the ban to Europe or other locations could cause significant logistical problems and deter some travel. Airlines that failed to satisfy new security requirements could still face future in-cabin electronics restrictions, the sources said.
European and U.S. officials told Reuters that airlines have 21 days to put in place increased explosive screening and have 120 days to comply with other security measures, including enhanced screening of airline passengers.
Reuters reported earlier this month that the United States had suggested enhancements, including explosive trace detection screening, increased vetting of airports' staff and additional detection dogs.
Since laptops are widely used in flight by business class passengers - who pay double or more than the average ticket price - the airline industry had feared expanding the ban could cut into revenue.
Airline officials said they will have to bear the brunt of expanded screening costs. Officials told Reuters they are concerned about adding new enhanced security measures to all of the roughly 280 airports that have direct flights to the United States rather than focus them on airports where threats are highest.
The U.S. imposed restrictions on laptops in March on flights originating at 10 airports in eight countries, including Egypt, Saudi Arabia, Kuwait, Qatar and Turkey. They came amid fears that a concealed bomb could be installed in electronic devices taken aboard aircraft. Britain quickly followed suit with a similar set of restrictions.
U.S. airline stocks were higher on Wednesday, with United Airlines up 1.4 percent and Delta Air Lines Inc and American Airlines Group each up 2.3 percent. None of the airlines immediately commented.
Homeland Security Secretary John Kelly said last week that U.S. authorities want to take the 10 airports off the restrictions list "by simply doing the kind of things that we're talking about here in terms of raising aviation security." He said the United States would boost security to a "much higher level."
Homeland security officials plan to announce that those airports can get off the list if they meet the new security requirements.
Starting in April, Kelly repeatedly said it was "likely" the laptop ban would expand to other airports - and even said in May the government could potentially expand the ban worldwide.
Kelly, who was speaking in Washington on Wednesday afternoon, said he planned a "step by step" security enhancement plan that included short, medium-term and longer-term improvements that would take at least a year to implement completely.
He said last week that airlines must take the issue seriously. "The threat is very real," he said.
Kelly met with senior airline executives in May and Homeland Security officials have had repeated meetings with U.S. airline executives.
Robert Mann, analyst at R.W. Mann & Co, said if U.S. officials had insisted on a expanded laptop ban, it could harm business travel.
He said new computer tomography or "CT" scanners being tested in Boston and Phoenix could help address long-term screening issues. Current screening of carry-on luggage "cant tell the difference between a block of cheese, a romance novel and a block of semtex plastic explosives because theyre all about the same density," Mann said.
One big issue facing policymakers was the potential safety implications related to past problems with laptop batteries and storing large numbers of laptops in the cargo hold.
U.S. Transportation Secretary Elaine Chao said at a June Senate hearing that lithium ion batteries on airplanes can be a problem and pose a fire risk. (Reporting by David Shepardson; Additional reporting by Alana Wise in New York and Julia Fioretti in Brussels; Editing by Steve Orlofsky and Dan Grebler)