[pdftex] Spacing between letters ---plain pdftex

[John R. Culleton]

There is a LaTeX sty that with some clumsiness will set a string of 
letters to a particular degree of "tracking" positive or negative. 
What I am wondering is if there is a primitive or plain tex value 
that I can modify for a given string to put letterspacing between 
glyphs such as is often used in a running head for fiction, often 
with smallcaps.  I am thinking of something like
\headline={\sc\foo 1.5 Here is My title} 

where \sc is a smallcap font and \foo is the parameter I need to reset 
to get more interglyph spacing. 
-- 
John Culleton