Did the US support Israel in 1973 when it was attacked by Egypt and Syria?
Yes. The United States supported Israel midway through the war. The Soviets had already provided assistance to the Arabs.
Iran and Israel have never actually gone to war. The two countries have fought a long, drawn-out proxy war for the last three decades, but never a direct conflict. You are likely asking about the Six Day War, but what is worth noting is that the only country that Israel attacked was Egypt. Then Syria and Jordan declared war on Israel, which prompted an Israeli response.