The forceful antitrust posture is a pillar of President Biden’s agenda to stamp out economic inequality and encourage greater competition. “Promoting competition to lower costs and support small businesses and entrepreneurs is a central part of Bidenomics,” a senior administration official said in a call with reporters.

The new guidelines would apply to all deals across the economy. But they highlight obstacles to competition among digital platforms, including how an acquisition of a nascent rival may be intended to kill off future competition. Such deals, known as killer acquisitions, are prevalent in the tech industry and at the heart of an F.T.C. antitrust lawsuit against Meta, which owns Facebook, Instagram and WhatsApp. The agency has accused Meta of buying Instagram in 2012 and WhatsApp in 2014 to prevent future competition.

The F.T.C. and Justice Department also said they would look at how companies used their scale, including their large number of users, to ward off competition. These so-called network effects have helped companies like Meta and Google maintain their dominance in social media and internet search.

The agencies also laid out ways in which mergers involving “platform” businesses, the model used by Amazon’s online store and Apple’s App Store, could harm competition. An acquisition could hurt competition by giving a platform control over a significant stream of data, the draft guidelines said, echoing concerns that tech giants use their vast troves of information to squash rivals.

“As markets and commercial realities change, it is vital that we adapt our law enforcement tools to keep pace so that we can protect competition in a manner that reflects the intricacies of our modern economy,” Mr. Kanter said in a statement. “Simply put, competition today looks different than it did 50 — or even 15 — years ago.”