The Republican Party served notice today that it will oppose President Carter's energy program on grounds that it unfairly penalizes poor people, large families and the middle class.

"Mr. Carter's energy program looks suspiciously like a backdoor way of raising enough taxes to pay for more government programs and still balance the budget," Republican National Chairman William Brock said in a speech coordinated with GOP congressional leaders. "We as Republicans will not be a party to such massive hoodwinking of the American people."

Brock delivered a systematic attack on the Carter energy plan at a meeting of the Republican National Committee. It was the first GOP national committee meeting since Carter was inaugurated and the first outside Washington in more than six years.

Before the meeting, Brock had been under fire from some GOP conservatives, notably Ronald Reagan, for failing to be critical enough for Carter. He was sharply critical by any measure today, and contended that the President had used the slogan of energy conservation merely as a ruse to raise taxes that would fund social programs.

"We reject the idea of income redistribution masquerading as energy conservation," Brock said.

Many of Brock's comments were based on the familiar Republican doctrine that the energy shortage is the fault of government price controls that discourage oil and gas production. He called upon the government to "lift the burden of regulation and let creative Americans respond to the pressures of a free marketplace."

But Brock also scored Carter for not seeking more assistance for public transportation and for unfairly penalizing low-income families that need their cars to travel long distances to work. And he was especially critical of the attempt to discourage use of larger automobiles.

"We will oppose any attempt by the government to deny people their family cars," Brock said. " . . . families with three or four children need a larger car, and they have every right to buy a car that is well-built and comfortable for their family's use.

Polls have shown that blue-collar families with middle-sized or larger cars are especially critical of Carter's plan to provide financial incentives for Americans to buy smaller automobiles.

The national committee also heard from Illinois Gov. James S. Thompson, who called on Republicans to abandon the use of "code words" that have little meaning to average Americans.

"What does 'free enterprise' mean to the average American voter?" Thompson asked. "Does it mean private corporations trying to outdo each other in servicing the public and real competition in the marketplace? Or does it mean entire industries which move their prices up and down in unison, allegations of price-gouging by oil companies, and Chevrolet engines turning up inside Oldsmobile cars?"

Thompson said the GOP should de-emphasize party labels and code words and recruit candidates who speak to the concerns of voters.

"Straight party-line voting is mostly dead or dying, and political party which doesn't recognize this courting the same fate," he said.