Which government agency primary mission is ensuring that enough money an credit are available to sustain economic growth without causing inflation

The correct answer is: "the central bank".

A country's central bank, which in the case of the United States is the Federal Reserve, is in charge of designing and implementing the monetary policy.

This consists on controlling the money supply mostly by influencing the interest rates charged for short-term borrowings, with the aim of ensuring economic growth and price stability, and hence, an stable domestic currency as well.

The government agency that has as primary mission ensuring that enough money and credit are available to sustain economic growth without causing inflation is the Federal Reserve. The Federal Reserve is the central banking of the United States. This means that it manages all concerning the country's monetary matters.