WASHINGTON — Senator McCain’s two chief policy planks in his general election platform thus far are drawing mixed reviews from some conservative activists and scholars, who are voicing approval of his prescription for health care while criticizing his proposal to combat climate change with a cap-and-trade program.

As the Democrats fight to the finish in their nomination battle, the presumptive Republican nominee has campaigned over the past three months with a mix of broad biographical speeches and more detailed policy addresses, much of which has been aimed at burnishing his image as a maverick and courting swing voters.

But turnout among the Republican Party’s conservative base will be key to Mr. McCain’s hopes in the fall, particularly in Southern states, where African-American voters are expected at the polls in record numbers to support Senator Obama if he is the Democratic nominee. Mr. McCain has acknowledged the need to solidify his standing among conservatives, saying on the stump that “our base is united, but they’re still not energized.”

In laying out specific plans on health care and climate change, Mr. McCain is taking on issues more traditionally associated with Democrats.

On health care, the Arizona senator is selecting from “within the general Republican quiver of arrows,” a prominent conservative activist and president of Americans for Tax Reform, Grover Norquist, said. Mr. McCain’s plan rejects the mandates for coverage backed by Democrats and encourages the purchase of private insurance by offering $5,000 refundable tax credits to families and eliminating the provision that exempts employer-provided health benefits from income taxes.

“I think it’s quite good,” Mr. Norquist said.

The change to the tax status of employer coverage has raised concerns that people with more expensive plans through their jobs could face higher taxes because the $5,000 credit ($2,500 for individuals) would not cover the cost incurred by scrapping the tax break associated with employer coverage. The United Mine Workers of America cited that provision specifically when it announced its endorsement of Mr. Obama last week. The union’s president, Cecil Roberts, said then that Mr. McCain’s plan would “impose a tax” on health care benefits that have been negotiated into employees’ contracts.

The McCain campaign has acknowledged that taxes could go up for some workers, but Mr. Norquist said that as long as the policy does not result in a net tax increase across the board, it could find support among economic conservatives in Congress, many of whom have signed his pledge to oppose all tax hikes.

“I’m assuming that McCain knows that 42 senators and 197 House members have signed the pledge and that he would make his fit so that it wouldn’t be a revenue increase and Republicans can join in their support,” Mr. Norquist said.

Mr. McCain has not signed the written pledge but has promised repeatedly on the campaign trail not to raise taxes.

His health care plan also drew praise from Pat Toomey, president of the Club for Growth, another influential Washington-based conservative group. Mr. Toomey said Mr. McCain’s approach to health care was “terrific.”

“I’m sure that there are things people can quibble about,” he said, “but on balance I think he is very much moving in the right direction on health care.”

The Club for Growth, however, has panned Mr. McCain’s proposal on climate change, which calls for a cap-and-trade program to limit carbon dioxide emissions. Under the plan, the government would impose a cap on greenhouse gas emissions, and companies would be able to buy and sell permits for emissions that exceed the cap.

Mr. Obama and Senator Clinton also have endorsed versions of a cap-and-trade system, with all three candidates championing it as a market-based solution to global warming. Critics say the costs would be exorbitant and that the technology does not exist to implement the plan.

“This is a very, very dangerous proposal, and it’s very unfortunate that Senator McCain has embraced this,” Mr. Toomey said. “Any cap-and-trade mechanism is going to be enormously expensive and devastating to economic growth.”

Mr. McCain has used his stance on climate change to break away from the Bush administration and woo independent voters and Democrats, and while his position is not new, his increased emphasis of it on the campaign trail risks alienating the conservatives who have long been wary of his maverick streak.

“It’s a tax levied in a very indirect and opaque way,” a resident scholar at the American Enterprise Institute, Kenneth Green, said of the cap-and-trade plan. “Fiscal conservatives are certainly not going to go for that.”

Mr. Toomey said that while Mr. McCain’s economic proposals have “generally been extremely good,” the climate change plan would “cause a lot of heartburn among free market conservatives.”

Despite his outspokenness on the issue during the campaign, Mr. McCain said yesterday that he plans to skip a key vote in the Senate next week on a bill that would place a mandatory emissions cap on greenhouse gases.

With attention on the economy and foreign policy in recent months, Mr. McCain has yet to focus heavily on social issues since clinching the Republican nomination. He outlined his philosophy on judges and railed against “judicial activism.” The speech was “well-received,” the head of the Southern Baptist Leadership Convention, Richard Land, said. Still, many social conservatives are eagerly awaiting Mr. McCain’s pick for a running mate.

“That could be make or break,” Mr. Land said.