President Reagan said today that he would "never" apologize to Egypt for the U.S. interception of a civilian airliner carrying four Palestinians who hijacked the cruise ship Achille Lauro.

Arriving at the air terminal here on a 4,500-mile daylong trek to help Senate Republicans, including incumbent Steve Symms (R-Idaho), Reagan was asked if the United States had anything to apologize to the Egyptians for concerning the interception.

"Never," he responded. Presidential spokesman Larry Speakes said, "We've said everything we need to say." The White House has indicated it sees no need to apologize to Egyptian President Hosni Mubarak, who has demanded an apology for the interception.

The issue of the Palestinian hijackers dominated Reagan's day. On arrival here he was greeted with a chant from one spectator, "Way to go with the PLO!"

Introducing Reagan later, Symms said the Sun Valley, Idaho, state convention of the Veterans of Foreign Wars had told him to tell Reagan of the hijackers: "Bring them to justice, give them a quick, fair trial, and hang 'em!"

In a speech to a Symms fund-raiser, Reagan declared twice, "There is a new patriotism alive in our country." He said he is "most proud" of the Navy fliers who intercepted the Egyptian plane last week, diverting the hijackers to a base in Sicily.

Departing from his prepared text, Reagan said, "They didn't have more than an hour's notice, and yet out there over the Mediterranean with all the air traffic that's going on in the area in the dark of night they were able to pick up the target plane and persuade it to land . . . ."

Reagan put emphasis on the word "persuade" and the crowd erupted in laughter and applause.

He said Symms, a former Marine, "understands that the fellas who intercepted those terrorists last week need to know that we're behind them all the way. And I can tell you, I'm mighty proud of the job they did, as I know you are."

The president did not mention U.S. frustration at Italy's release of a fifth Palestinian alleged to be the mastermind of the hijacking, Palestine Liberation Front leader Mohammed Abbas.

And Reagan said he would have "no comment" on the state of U.S.-Egyptian relations. Speakes said Reagan had laid out his "rationale and our views" on the interception in letters to Mubarak last weekend.

Speakes said the United States has also "made known to all governments in the region our views on the situation and that we will continue to be keenly interested in the apprehension" of Abbas.

Also today, Reagan took a new tack in defending his Strategic Defense Initiative, a proposed system to shoot down incoming ballistic missiles. Reagan stressed the economic aspects of his proposal and said it could be "the most cost-effective means of providing for our defense based on rapid advances in technology."

He also vowed "we will not bargain . . . away" the research and testing of the proposed shield against nuclear missiles.

Reagan's cross-country trip today was extraordinary because of its length at this early date. It is more than a year before the 1986 midterm elections, in which Republicans, who hold a 53-to-47 majority in the Senate, are defending 22 of the 34 seats at stake. The president was campaigning for the incumbents in two of those races, Symms and Robert W. Kasten Jr. (R-Wis.).

Reagan devoted part of his speeches to arguments for the missile defense program, which is expected to be a major point of discussion when he meets Soviet leader Mikhail Gorbachev in Geneva Nov. 19-20.

Often referred to as "Star Wars," the proposed system is now in the research phase. The Soviets have sought to stop it from going beyond research. Some U.S. officials have suggested that Reagan might agree to some restraints on the program in exchange for deep reductions in Soviet offensive missiles, although Reagan has insisted that the program is not a "bargaining chip."

In remarks today at Boise State University, Reagan said, "The idea of using American technological genius to develop a system to protect us against nuclear missiles is moral and in the fundamental interests of the United States and our allies, and the cause of peace. We will not bargain this research and testing program away when we get to Geneva."

Describing the program as a "historic turning point," Reagan said, "For the first time, energy and resources are being put to use in an attempt to find new technology that is aimed at saving lives.

"If we are successful, it will improve the opportunity for arms reduction because missiles, no longer the ultimate weapon they are today, will be more negotiable."

In his speeches today, Reagan referred to the economic burden of the arms race in arguing for missile defenses.

"Doesn't a cost-effective defense, allied with high technology, make sense in this day and age?" he asked his audience in Milwaukee. Reagan said he preferred to call the program the "Strategic Space Shield" because it is "a nonlethal weapon that is not going to kill people but that is going to kill antiballistic missiles before they can reach their target."

Reagan mistakenly said "antiballistic missiles" when he was referring to continent-spanning ballistic missiles.

In Boise, REagan said, "No one in a free country likes to spend money on weapons. I'd much rather see that money left in the hands of the people that worked for it."