<xsl:variable name="filter">
 <xsl:for-each....  //Recurso[condition]    (condition call to one 
template!!)

</xsl:for-each>
</xsl:variable>

I can't fill that in as I don't know what program logic you need, but
that will make a result tree fragment containing some number of
variables.

I thought the question was to find the number of elements generated
which would be

<xsl:variable name="total" select="count(x:node-set($filter)/*)"/>

where you have defined xmlns:x="..." whatever namespace your xslt system
docuemnts is needed for this extension function.

David