DES MOINES — Ron Paul’s college-aged volunteer army — a core of the powerful ground organization that is the envy of rivals — is descending on Iowa from around the nation to coax people to the state’s Republican caucuses as he seeks to pull off what only months ago seemed like an unthinkable victory here on Tuesday.

Four years after young people flocked to the state to help propel the campaign of Barack Obama, this radically different movement is embracing a 76-year-old veteran Texas congressman who is drawing supporters for his libertarian and antiwar views.

And they say they are under strict orders: To look, dress, shave, sound and behave in a way that will not jeopardize Mr. Paul’s chances. Even before flying here on their own nickel, some students said they had been instructed to cover up tattoos and told that their faces should be fresh-shaved or beards neatly trimmed, wearing only nice clothes that one described as “business casual.”