WASHINGTON - More than four-fifths of the US Senate have signed a letter urging President Barack Obama to quickly reach an agreement on a new defense aid package for Israel worth more than the current $3 billion per year.Eighty-three of the 100 senators signed the letter, led by Republican Lindsey Graham and Democrat Chris Coons. Senator Ted Cruz, a 2016 presidential candidate, was one of the 51 Republicans on board. The Senate's Democratic White House hopeful, Bernie Sanders, was not among the 32 Democrats."In light of Israel's dramatically rising defense challenges, we stand ready to support a substantially enhanced new long-term agreement to help provide Israel the resources it requires to defend itself and preserve its qualitative military edge," said the letter, which was seen by Reuters. It did not provide a figure for the suggested aid. Israel wants $4 billion to $4.5 billion in aid in a new agreement to replace the current memorandum of understanding, or MOU, which expires in 2018. US officials have given lower target figures of about $3.7 billion. They hope for a new agreement before Obama leaves office in January.The funding is intended to boost Israel's military and allow it to maintain a technological advantage over its Arab neighbors.The letter said the Senate also intends to consider increased US funding for cooperative missile defense programs, similar to increases in the past several years.Obama has asked for $150 million for such programs, but lawmakers are believed to be willing to send Israel hundreds of millions for programs like its Iron Dome air defense system and David's Sling medium- and long-range defense system. A source close to Prime Minister Benjamin Netanyahu said Israel is thankful to have tremendous support from both the Republican and Democratic parties.. Michael Oren who was ambassador to the US said, "We thank the senators for calling for a significant increase in military aid to Israel." He said he hopes a new agreement will be reached that will fit new realities in the Middle East. "President Obama's claim on his visit to Germany that the world is more peaceful today will not reassure the citizens of the Middle East, hundreds of thousands of whom have been murdered and millions displaced," Oren said. "Israel is dealing with many significant security challenges in the heart of the Middle East and I'm glad that this has recognized by the 83 senators who signed the letter."Zionist Union MK Nachman Shai said Netanyahu should stop playing off the current American government and the next one. "This is a dangerous step and a gamble that Israel cannot not allow itself to take," Shai said.Gil Hoffman contributed to this report.