Well, if your SVG is yet embedded in a fo:instream-foreign-object, your job will be quite eaier.
preserveAspectRatio must be used if you want that all descendants of svg element are transformed in the same way than svg element when viewbox is used (see [1])
I typically use preserveAspectRatio="none"
[1] http://www.w3.org/TR/SVG11/coords.html#ViewBoxAttribute

De : Samuel Remacle [mailto:sremacle@hotmail.com]
Envoyé : mercredi 27 juillet 2005 11:01
 My picture isn't an external graphic, it's an instream foreign object so I have to use the preserveAspectRatio attribute? And if I resize the whole svg document but I keep the same size for the differents elements (rectangles, circles, etc.) it doesn't matter? They will be resized? 
>From: "Pascal Sancho" <pascal.sancho@takoma.fr>
>Reply-To: fop-users@xmlgraphics.apache.org
>You cannot resize your picture directly if it is an external graphic (in FOP 0.20.5, scaling is not supported -- see [1])
>However, you can try this (I have never experimented it -- take care with namespaces):
>1. In your xslt, refer to your SVG document, using the document() XSLT function
>2. make a fo:instream-foreign-object as the SVG container
>3. transform your SVG xml as follows:
>     - change width and height attribute of the svg:svg element.
>     - if needed (that should be), add both viewbox and preserveAspectRatio attributes to your svg:svg element.
>     - copy the whole rest of xml
>[1] http://xml.apache.org/fop/compliance.html#fo-property-scaling
>   _____
> De : Samuel Remacle [mailto:sremacle@hotmail.com]
> Envoyé : mardi 26 juillet 2005 22:57
> I'm not sure you understood my problem, the SVG should be bigger in my application than in the PDF, so as it will be first viexed in the application, I need to resize it in the XSL-FO file, and I need to keep the proportions.
> So I'd like to no if there's a way to do that, does anyone know?
> >From: "J.Pietschmann" <j3322ptm@yahoo.de>
> >
> >Samuel Remacle wrote:
> >>application is ok. But after when I generate a PDF file from my
> >>application the SVG image is too big for an A4 document. So I'd
> >>like to know if there's a way to resize my SVG image keeping the
> >>proportions.
> >
> >Generate your SVG with a width and heigth attribute on your to level
> >svg:svg element, both in either cm, in or pt but not in pixel (no
> >measurement unit). The height and width should represent the actual
> >measurements in the PDF. Use the same heigth and width on the
> >fo:external-graphic or fo:instream-foreign-object in the FO source.