Which sentence in this excerpt from Franklin D. Roosevelt’s “Four Freedoms” speech suggests that the US government would gain more power to prepare for war?
The Congress, of course, must rightly keep itself informed at all times of the progress of the program. However, there is certain information, as the Congress itself will readily recognize, which, in the interests of our own security and those of the nations that we are supporting, must of needs be kept in confidence.
New circumstances are constantly begetting new needs for our safety. I shall ask this Congress for greatly increased new appropriations and authorizations to carry on what we have begun.
I also ask this Congress for authority and for funds sufficient to manufacture additional munitions and war supplies of many kinds, to be turned over to those nations which are now in actual war with aggressor nations.
Our most useful and immediate role is to act as an arsenal for them as well as for ourselves. They do not need man power, but they do need billions of dollars worth of the weapons of defense.
The time is near when they will not be able to pay for them all in ready cash. We cannot, and we will not, tell them that they must surrender, merely because of present inability to pay for the weapons which we know they must have.
I do not recommend that we make them a loan of dollars with which to pay for these weapons—a loan to be repaid in dollars.

In the sentence, Roosevelt's is stating that America need more power because the risk that now is facing -the second world war. The other sentences in the excerpt just serve to convince the congress to give more weapons to the allied nations so they can act as buffer while America gain more power to prepare to war. That is especially evident in the sentence: "Our most useful and immediate role is to act as an arsenal for them as well as for ourselves."

We can conclude that the sentence suggesting that the US government would gain more power to prepare for war is: New circumstances are constantly begetting new needs for our safety.