UPDATE 2-U.S. to unveil enhanced airline security plan to avoid laptop ban

(Adds more details of plans, prior security talks, Kelly quote)

WASHINGTON, June 28 (Reuters) - U.S. Homeland Security officials on Wednesday will unveil enhanced security measures for foreign flights arriving in the United States, in a bid to avoid an 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, sources said.

A European airline industry official told Reuters earlier this month that the United States had suggested enhancements including explosive trace detection screening, increased vetting of airports' staff and additional detection dogs. European and U.S. officials have held talks for months on expanded security measures.

The U.S. imposed restrictions on laptops in March on flights originating at 10 airports in eight countries that include 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.

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."

Homeland security officials plan to announce that those airports can get off the list if they meet the new security requirements.

Kelly, who is 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 completely implement.

He said last week that airlines must take this issue seriously. "The threat is very real," he said.

Airline 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. (Reporting by David Shepardson. Additional reporting by Alana Wise in New York; Editing by Marguerita Choy and Steve Orlofsky)