WASHINGTON - U.S. President Barack Obama on Tuesday blamed Republicans in Congress for the federal government shutdown, and defended his signature health care law.

Republicans in Congress "chose" the government shutdown that " did not have to happen," Obama said in a televised speech delivered in the White House Rose Garden on the first day of the first government shutdown in 17 years.

"They've shut down the government over an ideological crusade to deny affordable health insurance to millions of Americans," said the president.

"Many Representatives have made it clear that had they been allowed by (House) Speaker (John) Boehner to take a simple up or down vote on keeping government open with no strings attached, enough votes from both parties would have kept the American people 's government open and operating," he said.

The last time the government shut down was in 1996 during budget standoff between the Clinton administration and a Republican-controlled Congress. "Unlike 1996, our economy is still recovering from the worst recession in generations," Obama said.

"The longer this shutdown continues, the worst the effects will be," he said, urging Congress to "pass a budget" and "end the government shutdown."

Obama stressed that this shutdown is neither about deficits, nor about budgets, but about "rolling back the Affordable Care Act. " The law, commonly known as Obamacare, passed both chambers of Congress and was signed into law in 2010. The Supreme Court ruled it constitutional last year.

Obama said because of the funding sources, the health care law is not impacted by a government shutdown. "Even though the government is closed, a big part of the Affordable Care Act is now open for business," he said.

Americans in different states without health insurance can begin signing up for coverage through on-line exchanges. They have a six-month enrollment period for exchanges if they want to avoid a fine for not buying insurance, according to the law.

"Contrary to Republican claims, this law hasn't destroyed our economy. Over the past three and a half years, our businesses have created 7.5 million new jobs," the president said.

Obama told people who wish to get coverage through exchanges to visit the website, healthcare.gov. He even announced the hotline number twice.

After weeks of congressional back-and-forth, the Democrats- controlled Senate and the Republican-led House of Representatives failed to strike a last-minute deal to avert a government shutdown.

The House sought to make delaying or defunding all or part of the Obamacare a condition for approving government spending for the fiscal year that began on Tuesday, while Obama and his fellow Democrats refused to accept those conditions.

The White House Office of Management and Budget late Monday night ordered federal agencies to begin their plans for "an orderly" government shutdown.