President Obama has signed into the law the $US 787 billion economic stimulus package, predicting the package marked "the beginning of the end'' of America's worst economic slide since the 1930s-era Great Depression.

The passage and signing of the bill marks a major victory for the President who only took office less than a month ago.

The US head was in Denver for the signing and said the government has begun the essential work of keeping the American dream alive in our time.

However, Obama said the stimulus “doesn't constitute all we're going to have to do to turn our economy around”.

The package aims to reverse the economic free fall by pumping money into infrastructure projects, health care, renewable energy and conservation.

Workers will also see a tax break of $400 and couples will see that figure jump to $800.

It also gives tens billions of dollars to states to prevent deep spending cuts and more job layoffs. Consumers will receive tax incentives to buy first homes and new cars.

Poor people and laid-off workers will benefit from increased unemployment and food benefits and subsides for health insurance.

The bill even includes a “Buy American” provision which has already raised concern among US trading partners.

With the unemployment rate the highest it's been in 16 years, Obama has been traveling the country trying to lower expectations.

“None of this will be easy,” Obama said.