WASHINGTON— AT&T Inc. was asked Wednesday for more details on why it needs to acquire wireless operator T-Mobile, following the disclosure—accidentally released by its lawyers—that it could have expanded its high-speed wireless service to most Americans for one-tenth of the T-Mobile purchase price.

The request by regulators to AT&T highlights the central issue in the proposed $39 billion acquisition: whether the combined company would benefit consumers enough to overcome concerns that the deal could limit wireless competition.

Federal Communications Commission officials already are taking a closer look at AT&T's argument that the merger won't hurt consumers economically. The carrier filed economic data to the FCC earlier in the summer to bolster its case for the deal.

AT&T has argued federal regulators should approve its deal to acquire T-Mobile from Deutsche Telekom AG because it would allow the Dallas-based giant to expand its next-generation wireless network, known as LTE, to 95% of the population. That would enable Americans outside of big cities also to enjoy video downloads and other data-heavy services on their AT&T smartphones.

Expanding high-speed Internet service to all Americans is a top priority of Federal Communications Commission Chairman Julius Genachowski.