"I would say we're running out of targets," NBC News said it was told by an unnamed senior US official.
A Pentagon spokeswoman did not confirm the NBC News report.
“There have been no recent policy changes regarding US operations in Somalia,” Navy Commander Candice Tresch said in a statement.
“We continue to support the Federal Government of Somalia’s efforts to degrade Al-Shabaab.”
The US Africa Command has said its airstrikes have killed more than 150 Shabaab fighters in the past year, including a few of the group’s leading figures.
But the attacks appear to have had little impact on Shabaab’s 12-year-long armed campaign.
The group has shown it is still capable of carrying out bombings in the Somali capital that typically kill civilians as well as targeted adversaries.
Shabaab’s estimated 8,000 militants are also continuing to battle federal government troops and African Union forces in rural areas.
The US has about 500 ground-based personnel inside Somalia. The NBC News report said it is unclear how many US soldiers would remain in the country under the shift in strategy that the network says is being planned.
A draw-down of troops from Somalia would be consistent with President Trump’s recent moves to reduce US military involvement in countries where Islamist insurgents are active.
Mr Trump last month ordered the complete pullout of the 2000 US troops in Syria as well as a halving of the 14,000 troops based in Afghanistan.
Those decisions also follow reports that the Trump administration intends to shift its international focus from combating non-state operatives to countering perceived threats posed by China and Russia.
NBC News said that the shift in US posture in Somalia would result in the CIA taking over responsibility for directing air attacks on Shabaab targets.
“That would likely mean pulling out some US special operations forces that help pilots pinpoint targets, including for offensives carried out by African Union-led troops,” the US network reported.
“The CIA, unlike the US military, is not equipped to deploy hundreds of personnel on the ground to direct air strikes, and would almost certainly carry out fewer bombing raids,” NBC News reported.
The US conducted a total of 47 air raids on targets in Somalia in 2018, compared to 35 the previous year.
NBC News added: “The agency could target gatherings of Shabaab militants but would not be well-positioned to provide air power for a ground offensive by Somali government fighters or African Union troops, former officials said.”
The African Union Mission in Somalia (Amisom) currently numbers about 21,000 troops, including approximately 3500 Kenyan Defence Force soldiers.
Amisom has said it wants to reduce its presence in Somalia by gradually handing over to government forces the primary responsibility for fighting Shabaab.
But military experts acquainted with conditions in Somalia say the federal government is not close to being able to assume that role.