Alarmed by Israel's uncompromising attitude, the President sent on 28 May 1949 a note to Israeli Prime Minister David Ben-Gurion, expressing that he was not very pleased with the "excessive Israeli claims to further territory within Palestine" and its "rejection of the basic principles of the Resolution set forth by the GA on December 11th, 1948". The US position was that Israel should offer territorial compensation for any territory it had acquired outside the boundaries set forth in the UN resolution of 29 November 1947. The US warned that the Israeli attitude thus far at Lausanne "must inevitably lead to a rupture in those conversations" ... "and that a rupture arising out of the rigid attitude of the Government of Israel would place a heavy responsibility upon that Government and people". The US warned for a revision of its relation with Israel.[14]
When the US ambassador the next day handed over the telegram to Ben-Gurion the latter reacted with saying that US and UN had been unable to enforce the 29 November resolution and to prevent the Arab aggression. He stated that Israel was not established on basis of the resolution but on that of successful war of defence. Because the Arab states refused to make peace, he regarded refugees potential enemies of Israel.
It seems that the US position was that Israel was the aggressor and that Palestinians had rights which were violated in 1947 during the forced exodus and in 1948 when Israel declared independence. How was the US administration unable to enforce its position on a client state?
Why do you say Israel was a client state of the USA's back then?
Israel was not a client state at the time.
The US position was not that Israel was an aggressor. That would also be factually incorrect regarding who started the wars.
Wikipedia is notoriously unreliable on this subject. I would caution against conclusions being drawn from it. That's why it's not an acceptable source on this sub. The US position softened because Israel's argument of self-defense was accepted by much of the world community. And the Wiki page contains glaring inaccuracies like misrepresenting the nonbinding nature of the partition plan and talking about "Arab land" without defining it clearly. It also misrepresents Israel's position on borders and subsequently appears to contradict itself.