I have a Participant who would like to roll in funds from an International Pension Plan into a US 401(k) Plan. The Plan states it allows rollover from 401(a) or 403(a) Plans, excl. aftertax; 403(b) annuity contracts, 457(b) Plans, IRA or annuity under 408(a) or 408(b) and Roth 401(k). Would a foreign pension plan fall under the 401(a) or 403(b) section plans?

The other half of the equation is whether the distributing country would recognize the rollover and continue to defer taxation or whether they'd count it as a distribution.

As you don't specify the country of origin, here's a thread that asks the question re: UK plans. Some of the discussion and links might be helpful. http://benefitslink.com/boards/index.php?showtopic=35698

The foreign plan would have to meet the requirements of the applicable IRC section before the distribution would be eligible for rollover into a 401(k) plan. 401(a) requires that the Trust be created or organized in the US. With pension laws varying by country, I doubt you will find any foreign plans that satisfy US law unless they were specifically designed to do so.

From what I've read on BenefitsLink Message Boards, it may be possible if there is a treaty that allows it. (That's all I know about this topic.)

True. Unless the plan is established and maintained under the US tax Code and is an eligible retirement plan, it cannot be rolled over to a US plan.
Eligible retirement plan- for rollover purposes, is defined under 402(8)(b)

Edited to change 402(8)(b) to 402©(8)(B). Thanks jevd.