In the political trench warfare of the New Hampshire primary, a newly combative Ronald Reagan is taking the offensive against George Bush.

Speaking at public forums and news conferences along the Eastern seaboard, Reagan portrays the man who defeated him in the Iowa caucuses as a liberal who is out of step with the presumably conservative New Hapmshire electorate on the social issues of abortion, gun control, welfare and the Equal Rights Amendment.

Without saying anything about Reagan, Bush is trying to treat these attacks as evidence of desperation.

"When one person gets a little ahead you get people going for the jugular," Bush said Friday in a speech at Manchester High School.

Reagan raised the issues, which are among the favorites of his principal New Hampshire supporter, Manchester Union Leader publisher William Loeb, last Tuesday in a speech to the Franklin Rotary Club.

In response to a question about the differences between himself and Bush, Reagan said Bush favored a liberalized abortion law, a guaranteed-income welfare plan and the ERA and that he opposed them.

Later in a brief speech to the Hooksett Men's Club, Reagan said he had "forgotten" to mention that Bush also supports gun control while he opposes it.

And the next day, at a news conference in Greenville, S.C., Reagan explained his statement about gun control this way:his way:

"In 1968 he [Bush] voted for the gun control bill which is the last time I've heard any statement on that subject from him. I've always been against gun control. . . .What we did in California is the proper approach and that is, instead of trying to take guns from honest people, we passed a law that said, if a person is convicted of a crime and had a gun in his possession at the time of the crime . . ., add five to 15 years to the prison sentence."

Bush regards Reagan's statements on gun control and abortion as distortions of his position. When Bush was a Texas member of the U.S. House of Representatives in 1968, he voted in favor of a measure restricting mailorder sales of rifles and shotguns.

The Congressional Record shows that Bush voted for three conservative amendments that were incorporated into the bill, including one similar to the California gun control extolled by Reagan. This amendment extended the sentence of any person who commits a federal felony while using a firearm.

Bush was asked about his abortion vote in New Hampshire Thursday: "I oppose abortion. I oppose federal funding of abortion except in the case of rape, incest and the life of the mother. I do not favor a constitutional amendment to repeal the Supreme Court decision [which allowed a more liberalized standard of abortion] in that regard."

Reagan supports a constitutional amendment to repeal the court's 1973 decision. However, as governor of California in 1967, he signed a bill allowing abortions if "the mental health" of the woman might be affected.

More than a million abortions have been performed in California under this law, and Reagan now says the mental health clause became a loophole he never intended.

The other differences between Reagan and Bush are less equivocal. Bush does support ERA, while Reagan opposes it. And as a congressman, Bush voted for the Family Assistance Plan proposed by President Nixon which opponents termed the first step toward a guaranteed annual income. Reagan opposed the bill and urged Republicans to defeat it.

Differences also have developed over President Carter's call for a peacetime draft registration and the registration of women.Reagan opposes and Bush supports these measures.

Without mentioning his principal opponent by name, Bush suggests that some of Reagan's foreign policy pronouncements are dangerously hawkish.

"Ronald Reagan has proposed a blockade of Cuba to stop Russian aggression halfway around the world," Bush said Friday in Manchester. "I would not. I don't believe that is right. I don't know where all the ships would come from to do it. I don't quite see the relevance, I am not soft on Castro. I believe Castro is trying to export revolution . . . but there has to be some adherence to international law.

"I can see some vague relationship, inasmuch as Russia is training Cubans to be their surrogates in Africa, but I don't see why when the Soviets are aggressors in Afghanistan we declare war on China. That's not my conception of how one uses power or how one makes foreign policy decisions."

Reagan has said the Cuban blockade is merely "one of the options" he would consider as president. He also has suggested that the United States establish a military presence with bases in the Middle East, a proposal Bush rejects.

These conflicting views may be building toward a confrontation in a forum among the seven GOP presidential candidates in Manchester Feb. 20 and even more so if a proposed debate between Reagan and Bush in Nashua comes off on Feb. 23.

But an attack style does not appear natural to either candidate. In past campaigns Reagan has tried to avoid criticizing opponents, especially other Republicans. Bush was the only one of the six candidates in the Iowa debate to refrain from criticizing Reagan.

The refusal of Bush to go on the attack is seen as an asset by his New Hampshire chairman.

"How do you think he's gotten as far as he has?" said former New Hampshire governor Hugh Gregg when a reporter asked him why Bush wouldn't directly respond to Reagan. Gregg, who was Reagan's New Hampshire chairman in 1976, also said Reagan would do badly as an attack candidate.

"That's not his style,; Gregg said. "If he goes onto the attack, he'll get killed."

At times Friday Bush seemed to be reminding himself not to take Reagan's comments personally. Bush recalled, from his baseball playing days at Yale, that athletes who are oversensitive to criticisms from the other team are known as "rabbit ears."

"Politics is that way," Bush said. "I went to Iowa as an underdog and I beat Ronald Reagan, a great big frontrunner. You begin to get a lot of criticism from other candidates and other sources and the thing to remember is not to have rabbit ears, not to stand out there and every time somebody criticizes you unfairly, answer them back.

"You stand on your record and on your experiences; you don't try to tear down the other candidates and I won't."

So far, Bush does not seem to have been seriously damaged by the revival of charges in a Los Angeles Times story Thursday, that he failed to report contributions in a 1970 Senate campaign in Texas. He was asked about the story only once in two days of New Hampshire campaigning, although a Nashua leader in the Bush organization said his telephone workers were picking up "some static" on the issue.

When Reagan was asked about the accusation today in Hooksett, he said that "the people had a right to know" about the story and that "all the details should come out." But he said he did not know any more about it than he had read.