Federal and state governments are entering the home stretch in the race to carry out the most important health care reform in more than four decades. The most pressing task is to establish new health care exchanges, the electronic marketplaces in which consumers will be able to compare and buy insurance plans just as they buy airplane tickets or rent cars on the Internet.

The exchanges are scheduled to start enrolling people on Oct. 1 in policies that will become effective in January 2014. It is a challenging task but not an impossible one, as long as Americans have a chance to learn how they can benefit from the coverage and from sliding-scale subsidies provided by the federal government under the Affordable Care Act.

To their shame and discredit, Republicans are trying to block efforts to inform people about the law and are using scare tactics to keep them from enrolling. The Republican mantra is that the nation will face economic and medical catastrophe — a “train wreck,” they say — unless health care reform is stopped in its tracks.

Their tactics are despicable. When Kathleen Sebelius, the secretary of health and human services, revealed that she was talking with the National Football League and other athletic organizations about ways to inform their fans about insurance on the exchanges, the two highest-ranking Republican senators wrote a threatening letter that caused the league to back off.

Crossroads GPS, a conservative group co-founded by the Republican strategist Karl Rove, has been running a video comparing the law to a tornado that will produce “a rising tide of health care costs” and leave “nobody safe from its wrath.”

Top officials in Ohio and Indiana who oppose the law have issued dire, misleading forecasts — roundly debunked by analysts — that the law will raise premiums to astronomical levels. And the House Republican Conference is advising its members on how to organize “emergency health care” town hall meetings during the August recess to denounce the law. The goal is to ignite passionate opposition to the measure, like that stirred up by Tea Party activists at town hall meetings in the past.

In virtually no case do Republicans ever mention that millions of people who lack health insurance or have lousy policies could obtain comprehensive coverage on the exchanges and that most of them would qualify for federal subsidies to lower the cost.

Many states, mostly governed by Republicans, have refused to set up their own exchanges and have left the job to the federal government. (Many states also have refused to expand their Medicaid programs to cover more of the uninsured, but that is a separate issue.)

The exchanges will need to enroll millions of people so that insurers have a large enough pool to drive down premiums, and they will need enough young, healthy people to help offset the cost of insuring older and sicker people. The Congressional Budget Office has predicted that some seven million Americans will gain coverage through the exchanges in 2014.

In a report last month on exchanges being set up by the federal government, the Government Accountability Office judged that “much progress has been made” but that “much remains to be accomplished.”

The administration is mounting a fierce campaign to publicize the law and spur enrollment by working with community clinics and other groups, as well as by providing grants to train workers to help people fill out the forms.

In the meantime, Republicans in the Senate are threatening to oppose any spending bill that provides a single cent toward health care reform, a threat that could shut down the government this fall. House Republicans are planning their own draconian cuts in funding to carry out the law. The Republicans’ determination to destroy health care reform has become an obsession that, if successful, will deprive millions of Americans of health insurance they need and want.