Question about SELECT and ORDER BY

Hi,

I have two tables:

table1 (attr1 text, attr2 int4)

table2 (attr1 text, attr3 int4, attr4 bool)

I have a query:

SELECT table1.attr1 AS ALIAS, attr2 from table1 UNION ALL
SELECT table2.attr1, attr3 from table2 ORDER BY ALIAS;

I that syntax all is OK.
I want to have a result from ORDER BY length(ALIAS), but this is imposible.

When ORDER BY clause is in format ORDER BY length(attr1), the result is not
ORDERED BY length of attr1.

What can I do? Are anybody have an idea?

Vladimir