NO.
It would violate the 4th Amendment. Federal agents are not permitted to search people without a warrant (or the searchee's permission), especially outside of federal facilities. If I'm merely travelling from here to there via privately-owned vehicle (airplane), and boarding the vehicle at a city-owned facility (airport), and I'm exhibiting no suspicious behavior, it's none of the fed's d@mn business what I'm carrying.
Privately-hired guards are acceptable (barely) as the matter involves private companies & indivduals doing business (as in: I have the right to deny someone admission to my house or store if they refuse a security search). Federal agents are prohibited from trumping that search process with their own forced & arbitrary searches.
Bill Of Rights, Amendment IV: "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."