WASHINGTON — President Barack Obama today will ask Congress for greater power to shrink the federal government, and his first idea is merging six sprawling trade and commerce agencies whose overlapping programs can be baffling to businesses.

Obama will call on Congress to give him a type of reorganizational power last held by President Ronald Reagan.

The Obama version would be a so-called consolidation authority allowing him to propose mergers that promise to save money and help consumers. The deal would entitle him to an up-or-down vote from Congress.

It would be up to lawmakers, therefore, to first grant Obama this fast-track authority and then decide whether to approve any of his specific ideas.

In an election year, Obama’s motivation is about improving a giant bureaucracy — but that’s hardly all of it.

Politically, his plan would allow him to do so by putting the onus on Congress and in particular his Republican critics in the House and Senate, to show why they would be against the pursuit of a leaner government.

Obama also has an imperative to deliver. He made a promise to come up with a smart reorganization of the government in his last State of the Union speech. That was nearly a year ago.