Let's look at this from another angle.
The US might not want an India that's totally dominant in military strength for the region, just incase if India decides to flex its military muscle in the future.
By providing aid and weapons to Pakistan, the US creates a weaker, but effective deterrance to India.
The Pakistanis want to purchase 71 new F-16 block 52's, and upgrade its existing 30-40 F-16 block 15 fleet to MLU status:
And the US is offering a 5-year, $3 billion assistance package to Pakistan:
"Pakistan has received significant loan/grant assistance from international financial institutions (e.g., the IMF, the World Bank, and the Asian Development Bank) and bilateral donors, particularly after it began using its military/financial resources in the war on terror. The United States recently pledged $3 billion for FY 2005 to FY 2009 in economic and military aid to Pakistan. In addition, the IMF and World Bank have pledged $1 billion in loans to Pakistan. In 2004 to 2007 alone, the World Bank has pledged over $500 million in investment projects."
I foresee the US selling Pakistan new, Block 52 F-16's with a limited number of AIM-120 AMRRAMS and precision air to sea/ground munitions in the future. The number of aircraft and missiles transferred would be limited, but the systems are combat proven and will give the Indian AF something to worry about.