[pdftex] How to typeset "1ª" in pdftex

[Maurí­cio]

Hi,

I would like to typeset "1ª". How can I do that? I tried something
like \raise 0.5ex {\underbar{a}}, but I would like the 'a' to be
smaller than the current font. How can I do that?

Thanks,
Maurício