The next President pro tempore question

[MASHED POTATOES. VOTE!]

If the Democrats retain the Senate, Inouye will continue to serve as PPT as the most senior Democrat, serving since 1963, with the second, Leahy, entered the chamber 12 years later.

But if the Republicans would take a control, who'd be the next PPT? Lugar and Hatch were sworn-in the same day (January 1977) and according to the most sources, Lugar have a seniority edge, thus is a presumed PPT of GOP-controlled Senate. However, as I was reading wikipedia, I found this, granted, one year old, link.

So, can someone familiar with a seniority issues explain it to me? I'd still say Lugar, but what if it would be openly questioned? 

[feeblepizza]

According to Senate and GOP Caucus rules, Lugar is most senior.

[True Federalist (진정한 연방 주의자)]

Giving to the longest serving Senator of the majority party is only a tradition.  However, since the post has no real duties but an increase in salary I can see why both men would covet it.  If Hatch isn't planning on running in 2012, I can see a way for him to get the position if he really, really, wants it.  If the GOP does tale back control, it's likely to be by the margin of 51-49.  If Hatch ignores the likely choice of the GOP caucus and the Democrats are willing to back him, he could end up as President pro tem after a 50-50 tie leaves the choice of PPT in Biden's hands.