WASHINGTON — Senators pressed top antitrust regulators on Tuesday to aggressively investigate the power of the country’s biggest tech companies, with some lawmakers questioning whether the officials had the will or resources to take on Silicon Valley’s richest businesses.

In the regulators’ first hearing since the Federal Trade Commission and the Justice Department divided up antitrust responsibilities for Amazon, Apple, Google and Facebook, lawmakers pushed for assurances that the agencies would provide vigorous oversight of the companies.

But the regulators — Joe Simons, the chairman of the trade commission, and Makan Delrahim, the top antitrust official at the Justice Department — offered few details about their inquiries into the industry. That frustrated some of the lawmakers at the hearing, held by the Senate Judiciary subcommittee on antitrust.

“The fact that you’re coming here without any specifics I think reinforces the impression that federal antitrust enforcement is an empty suit,” said Senator Richard Blumenthal, a Democrat from Connecticut. “What the public sees is a facade with respect to Big Tech — and no immediate prospect of urgency or active enforcement.”