PORTLAND, Maine (AP) — Facing a public still wary of his massive health care overhaul, President Obama urged Americans not to judge the nearly $1 trillion legislation he signed into law last week until the reforms take hold.

During an enthusiastic, campaign-style appearance in Maine’s largest city, Obama mocked the pundits and pollsters who say he isn’t getting a boost from his yearlong campaign to pass the sweeping reform.

‘‘Every single day since I signed the reform law, there’s been another poll or headline that said, ‘Nation still divided on health care reform. Polls haven’t changed yet.’ Well, yes. It just happened last week,’’ Obama said to laughter.

He continued: ‘‘Can you imagine if some of these reporters were working on a farm and you planted some seeds, and they came out the next day and they looked and — ‘Nothing’s happened. There’s no crop. We’re going to starve. Oh, no! It’s a disaster!’ It’s been a week, folks. So, before we find out if people like health care reform, we should wait to see what happens when we actually put it into place. Just a thought.’’

The president’s overhaul extends health coverage to 32 million people who are uninsured and will shape how almost every American receives and pays for medical treatment. Some aspects of the plan go into effect this year, but president himself has said it could take four years for the full overhaul to take hold.

Obama’s trip to Portland took him to the home state of two moderate Republican senators, Susan Collins and Olympia Snowe, whose votes for the legislation the president ardently sought but ultimately could not win. The White House said both senators were invited to attend the event, but neither did.

During the speech, one in a series of appearances to sell the health reforms, Obama focused on his health plan’s short- and long-term impact on small businesses, many of which have suffered during the economic downturn.

Under the plan, businesses that have 25 or fewer employees with average annual wages of less than $50,000 will receive tax credits this year if they provide health care coverage to their workers. Those credits are expected to increase by 2014, with 4 million small businesses benefiting, according to the White House.

‘‘This health care tax is pro-jobs, it’s pro-business and it starts this year,’’ Obama said.

Also starting in 2014, companies with up to 100 employees will be able to buy insurance through new state-based purchasing pools, or exchanges, with the goal of giving small businesses the same kind of purchasing power as larger companies. About 22 million self-employed Americans will also be able to purchase insurance through the exchanges.

Congressional Republicans were united against the law and many predict that Democrats who voted for it will be dragged down in the November elections. Some Republicans are calling for repeal, and Obama said they should ‘‘go for it’’ but also be prepared to explain why they want to take away tax credits, a ban on denial of coverage for pre-existing conditions and other popular elements of the new law.

‘‘If they want to have a fight, I welcome that fight. Because I don’t believe the American people are going to put the insurance industry back in the driver’s seat,’’ he said.

After speaking in Maine, Obama made an unscheduled stop in Framingham, Mass., about 20 miles outside Boston, to get a briefing on emergency response efforts to the flooding in the state. He then headed to Boston to attend two fundraisers for the Democratic National Committee.

His trip comes as much of the Northeast is suffering through devastating flooding caused by record-setting rainfall.

One of Rhode Island’s Democratic congressmen, Rep. Jim Langevin, sent a letter to the White House on Thursday requesting that Obama view the damage to that state during his travels. Homeland Security Secretary Janet Napolitano plans to travel to Rhode Island on Friday.