Use PROC TEMPLATE to create a style that redefines the font sizes for the FONTS list. Most PROCs and the DATA step with FILE PRINT ODS, use the following fonts: DOCFONT, HEADINGFONT and TITLEFONT. The below code shrinks ALL definitions by 2pt (points).

proc template;
   define style Styles.smaller;
     parent = styles.rtf;
      replace fonts /
         'TitleFont2' = ("Times Roman",10pt,Bold Italic)
         'TitleFont' = ("Times Roman",11pt,Bold Italic)
         'StrongFont' = ("Times Roman",8pt,Bold)
         'EmphasisFont' = ("Times Roman",8pt,Italic)
         'FixedEmphasisFont' = ("Courier",7pt,Italic)
         'FixedStrongFont' = ("Courier",7pt,Bold)
         'FixedHeadingFont' = ("Courier",7pt,Bold)
         'BatchFixedFont' = ("SAS Monospace, Courier",5pt)
         'FixedFont' = ("Courier",7pt)
         'headingEmphasisFont' = ("Times Roman",9pt,Bold Italic)
         'headingFont' = ("Times Roman",9pt,Bold)
         'docFont' = ("Times Roman",8pt);
  end;
run;

ods rtf file="file.rtf" style=styles.smaller startpage=no;

proc print data=sashelp.class(obs=2);
run;

ods rtf style=styles.rtf;

proc print data=sashelp.class(obs=2);
run;

ods rtf close;

For code showing how to do this in the PRINTER family (PCL, PDF, or PS) destinations, see FAQ 4197.