The 2 men, Arian Taherzadeh and Haider Ali, were arrested Wednesday in D.C. and charged with impersonating federal law enforcement agents -- prosecutors claim they posed as Department of Homeland Security agents, and then tried to hook up the First Lady's Secret Service agents.

Taherzadeh allegedly offered a $2,000 assault rifle to one of Dr. Biden's agents -- and now 4 of her agents are on administrative leave pending an investigation.

Prosecutors claim the federal posers also lavished Secret Service agents and a real DHS employee with iPhones, a drone, a flat screen TV, a generator, an assault rifle storage case, surveillance systems and law enforcement equipment.

Prosecutors says one Secret Service agent, who was assigned to the protect the White House, lived rent-free in a 3-bedroom luxury apartment provided by Taherzadeh ... where the rent typically runs more than $48,000 a year.

The FBI says Taherzadeh and Ali pretended to be agents from a fake DHS task force investigating violence at the Jan. 6 riots ... and the feds say the men used insignias and firearms used by federal agents to keep up the act.

Prosecutors believe the men were posing as agents "to ingratiate themselves with members of federal law enforcement and the defense community."

The alleged impostor act began to unravel last month, when a U.S. Postal Inspector looked into a possible assault on a letter carrier at the apartment complex where Taherzadeh lived, with the men allegedly identifying themselves as members of the non-existent task force.