AHD:
in·ter·gen·er·a·tion·al
ADJECTIVE:Being or occurring between generations: “These social-insurance programs are intergenerational and all Americans benefit from their success” (Claude D. Pepper).

"The implicit intergenerational contracts that that are sometimes attributed to pay-as-you-go pension schemes are strained when the generations differ considerably in size."
Workers versus pensioners By David Thomson, Christoph Conrad, Centre for Economic Policy Research (Great Britain)
http://books.google.de/books?id=8Du8AAAAIAAJ...

"Revising the Intergenerational Contract"
http://www.brookings.edu/articles/2008/summer...

"THE INTERGENERATIONAL CONTRACT"
Section in UN World Your Report 2003
http://www.un.org/esa/socdev/unyin/documents/...

FWIW, "pact across the generations" has only 2 Google hits: this thread and a book. In contrast:
3,880 for "inter-generation contract"
4,400 for "inter-generational contract"

I'd rather add 'intergenerational contract' to LEO. Moreover, the current entry is marked wrongly as [finan.]: Siehe Wörterbuch: Generationenvertrag The term is not directly related to financial markets but is used mostly in political sociology. It should be marked [sociol.].

'What has happened to the inter-generational contract? Strange that many members of the cabinet benefited from student grants, but now think it is not suitable for today's students.'
http://news.bbc.co.uk/2/hi/talking_point/1816...

"inter generational contract" +bbc
ergibt über 300 Google-Treffer, das schein also, zumindest in GB, ein üblicher Ausdruck zu sein.

M-W:
inter-
1 : between : among : in the midst intercrop interpenetrate interstellar
2 : reciprocal interrelation : reciprocally intermarry
3 : located between interstation
4 : carried on between international
5 : occurring between interborough : intervening interglacial
6 : shared by, involving, or derived from two or more interfaith
7 : between the limits of : within intertropical
8 : existing between intercommunal intercompany
# in*ter*gen*er*a*tion
# in*ter*gen*er*a*tion*al

AHD:
intergenerational
ADJECTIVE: Being or occurring between generations: “These social-insurance programs are intergenerational and all Americans benefit from their success” (Claude D. Pepper).

CALD:
inter- (BETWEEN)
prefix
used to form adjectives meaning 'between or among the stated people, things or places':
interactive television
intergovernmental meetings
intercontinental missiles

According to the dictionaries it should be spelled with no hyphen.

In any case, 'intergenerational contract' is far more common than the current LEO entry.

Google hits:
3.560 for "intergenerational contract"
1.230 for "inter-generational contract"
613 for "inter-generation contract"
302 für "intergeneration contract"