In a televised interview on Monday, Foreign Minister Ahmad Mahir explained Cairo's decision to snub some of the world's richest countries.
He said Arab identity should not be dissolved into a US-backed Greater Middle East Initiative (GMEI) and that other Arab states attending the Group of Eight meeting would make that clear.
The US initiative, designed to counter growing Islamist movements, was also criticised as an attempt to impose reform from abroad while not addressing key regional issues such as the Palestinian-Israeli conflict.
Other Arab countries to pass on the summit may include Tunisia and Qatar.
However, Saudi Arabia, Jordan, Yemen, Bahrain and Morocco are all expected to attend the three days of talks that begin on 8 June in the Sea Island, Georgia.
The G8 comprises the leading industrialised nations - Britain, Canada, France, Germany, Italy, Japan, Russia and the US.
Asked how serious a problem it was for Egypt and Tunisia to turn down the US invitation, White House spokesman Scott McClellan told reporters: "We believe very strongly that it's important to support the calls for reform in the region."
"This initiative is about supporting efforts under way for reform in the region by the people in the region. And we want to support their efforts, not impose anything on them."
US officials have said the US and EU had narrowed differences over the GMEI, but were still at odds about how it fitted with the Arab-Israeli peace process and the conflict in Iraq.