The font tag is deprecated. You shouldn't use it. If by "can't use CSS" you mean that you don't know how to do it, then I'll show you. There isn't really any reason you can't use CSS, since all modern browsers that I know of support it fine. Using the font tag is considered outright wrong by people today. Unless this is a homework assignment or something and your teacher is demanding that you use no CSS, you should use CSS.

Code:
<a href="blah" style="font-size: 25px;">Blah</a>
<a href="blah" style="font-size: 25px;">Blah</a>