(CNN) -- A new poll finds that many Americans are not optimistic about what the GOP health care bill will do to their coverage.

Although President Donald Trump and Republicans in Congress promise that their plan will cover more people and cost less, nearly half of Americans don't believe it, according to a Kaiser Family Foundation poll released Wednesday.

And while many Republicans are confident that defunding Planned Parenthood is the right move, the greater majority oppose that idea, it says.

This is the first poll on the legislation from the nonpartisan Kaiser Family Foundation.

The organization polled Americans from March 6-12, before the nonpartisan Congressional Budget Office released an estimate Monday predicting that -- unlike Obamacare, which brought the uninsured rate to an all-time low -- the GOP bill will send the country's uninsured rate higher than before the Affordable Care Act.

That change could be immediate for 14 million Americans who would lose their insurance next year, according to the report.

Of the more than 1,200 nationally representative random Americans polled, Kaiser found that 48% think the GOP plan will cover fewer people, compared with the one in five who said the bill would increase coverage.

Trump and congressional Republicans have vowed to lower costs with their health care plans, but nearly half (48%) of Americans polled think the bill will increase costs for people who buy their own insurance, while 23% think it will lower costs.

The thinking falls along partisan lines. Of those who think the bill will lower costs, 46% are Republicans. Most Democrats -- 71% -- expect higher costs. Independents tend to side with the Democrats; 47% think costs will increase.

Most people think the GOP bill will raise costs for both younger and older people, city and rural residents, and people who are poor. The public is divided on whether the costs will go up for the rich.

Overall, the public is torn over health care legislation: Fifty-one percent think the Affordable Care Act should not be repealed, but 45% think it should.

Among those favoring repeal, 24% want Congress to come up with a plan to replace it before they act to change it, but 19% want an immediate vote like House Speaker Paul Ryan argues is necessary.

Coverage of pre-existing conditions, which would not change under the proposed GOP legislation, is also on Americans' minds. Most people think coverage will stay the same (45%), but 32% still think fewer people with pre-existing conditions will be covered than now, and 15% think more people with pre-existing conditions will have coverage.

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