returning count(*) when it is > 1, else -1

Hi all. Im triyng to implement this in plain sql.
The only thing i have working is

select case when (select count(*) from test where id=$1 )   > 0 then (select count(*) from test where id=$1)   else -1
end;
 

But it does a doble count(*) that i must avoid.
I cant refer to the 'first' count like
select case when (select count(*) from test where id=$1 ) AS total   > 0 then total   else -1   end;

Because i have "Syntax error near AS"

I have a plpgsql version of this, but i swear to my boss that it can be
done is plain sql. Please tell me that im right :)

Thanks!
Gerardo