WASHINGTON — Almost two years after outlining a broad strategy intended to strengthen the security of the nation’s computers and networks, the Obama administration said Thursday that it was sending proposed legislation to Congress that would strengthen penalties for any invasion of private computer systems.

But the White House, in a briefing for reporters, said it had elected not to seek authority for stringent top-down regulations that would require companies to erect specific barriers to computer intrusions — which corporations feared would be enormously costly and soon be outdated.

Instead, the administration is hoping to offer incentives that will persuade private industry to improve computer security voluntarily and have those standards reviewed by the Department of Homeland Security.

“The private sector has a huge incentive to secure its own systems and an incentive to do that work better by sharing that information more broadly,” said Gregory T. Nojeim, senior counsel for the Center for Democracy and Technology, a policy group here.