problem with underline using babel

Question

My latex document is in hebrew and english
those are my headers :

\documentclass[greek, english, hebrew]{article} % <- here
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[greek, english, hebrew]{babel} % <- and here
\usepackage{amsmath}

and when I try to

\underline{x^2}

I'm getting those errors:

Missing $ inserted. $\underline{x^2}
Missing } inserted. $\underline{x^2}
Missing $ inserted. $\underline{x^2}
Missing } inserted. $\underline{x^2}
Missing $ inserted. $\underline{x^2}
Missing $ inserted. $\underline{x^2}
Extra }, or forgotten $. $\underline{x^2}
Extra }, or forgotten $. $\underline{x^2}

without

\usepackage[greek, english, hebrew]{babel}

underline works but hebrew not

any tips? thanks!