But executive orders on the matter have been put on hold amid pushback from national security agencies concerned about the consequences of such a move, they said.
The officials said drafts of executive orders have been written asking the State Department to study possible designations of the groups.
They said the White House had originally planned for President Donald Trump to sign the IRGC order Monday during his visit to CENTCOM in Florida, but the plan was scrapped after the State and Defense Departments voiced what one senior official called "serious objections."
It is unclear when the orders would be signed.
Several officials said the fact the orders have been put on hold was an encouraging sign the inter-agency process was working, with the White House now considering the expertise of career officials after failing to consult national security agencies before rolling out new immigration policy to disastrous results.
Chief among the concerns of designating the IRGC as a terrorist organization, officials said, is the difficult position such a designation would create for Iraqi Prime Minister Haider al-Abadi. Abadi is a key partner with the US in the fight against ISIS, but Iraqi forces also rely on support from the IRGC.
There is also concern about US military and embassy personnel in Iraq who could become a terror target.
The move would be largely symbolic, however, because as a designated "state sponsor of terror," the Iranian government and its entities, including the IRGC, are already under sanctions by the US and it's not clear whether they would be expanded.
The IRGC is Iran's premier security institution, with influence over practically every aspect of Iranian life. Tied to the country's hardliners, the corps manages Iran's ballistic missile program and is responsible for training Iranian proxies like Hezbollah through its Qods Force. The IRGC is also a powerful economic player, with control over many Iranian industries.
For years, the US has imposed tough sanctions on individuals and groups with links with the IRGC, and several administrations have considered the group a terrorist organization in previous executive orders. Most recently, the Trump administration announced sanctions on individuals who support the Qods Force on the heels of Iran's ballistic missile test last week.
But it is unclear whether as a state entity, the IRGC would meet the legal criteria to be designated a Foreign Terrorist Organization. State Department lawyers have argued that the designation could open the United States and Israel to retaliation in kind from Iran, which might designate the CIA or the Israeli Defense Forces, for example, as terrorist groups subject to punishment.
The White House is also weighing whether to slap the same designation on the Muslim Brotherhood. Trump's advisers consider the Muslim Brotherhood a radical Islamist group and Trump has suggested the Brotherhood is intent on spreading Shariah law in the US.
At his confirmation hearing last month, Secretary of State Rex Tillerson grouped the Muslim Brotherhood and al Qaeda together as "agents of radical Islam."
US allies in Egypt and the United Arab Emirates have urged Trump to designate the Brotherhood as a terrorist group. But officials told CNN that career diplomats at the State Department and National Security Council have questioned the legal basis for such a designation and have expressed concern the move could alienate other Arab allies, where the Muslim Brotherhood is a pillar of Arab society.
The Brotherhood, a political and social organization that calls for a society based on Islamic law, renounced violence decades ago and affiliated groups in Turkey, Tunisia and Morocco have joined the political process. Most notably, the Brotherhood won Egyptian elections in 2012 after the fall of Hosni Mubarak and ruled the country until President Mohammed Morsi was overthrown in a popular revolt supported by the military.
But splinter groups, in particular the Palestinian group Hamas, have turned to terrorism.
The process by which the State Department determines whether a group qualifies as a Foreign Terrorist Organization is complicated and usually takes several months. After exhaustive research of the threat posed by a group being considered for the designation, both from US databases and working with foreign governments, the State Department sends a proposal to other relevant agencies -- such as the NSC and Treasury -- for input before State Department lawyers sign off on whether the group meets the criteria. The final call, though, would likely be made by the White House.
The administration could punt to Congress on the Muslim Brotherhood matter. Last month, Republican Sen. Ted Cruz of Texas reintroduced legislation last month calling on the State Department to designate the Brotherhood as a terrorist organization or explain why it would not.