After lagging behind other countries for years, commercial drones in the U.S. are expected to begin limited package deliveries within months, according to federal regulators and industry officials.

The momentum partly stems from stepped-up White House pressure, prompting closer cooperation between the government and companies such as Amazon.com Inc. seeking authorizations for such fledgling businesses. The upshot, according to these officials, is newfound confidence by both sides that domestic package-delivery services finally appear on the verge of taking off.

Earlier promises of progress turned out to be premature. The green light could be delayed again if proponents can't overcome nagging security concerns on the part of local or national law-enforcement agencies. Proposed projects also may end up stymied if Federal Aviation Administration managers don't find creative ways around legislative and regulatory restrictions such as those mandating pilot training for manned aircraft.