Menachem Begin's new friend didn't attend but there were plenty of official substitutes at the National Portrait Gallery dinner in his honor on what he called the second "good" day of his Washington visit.

"A man with a warm heart and the most wonderful simplicity of manner," the Israeli prime minister said of the absent President Reagan in his toast before a black-tie crowd of 180 top-level Israeli and American leaders last night.

Vice President George Bush lost no time in agreeing. He assured Begin that in Reagan "Israel has a first-class friend," an opinion that seemed to be borne out by the new U.S.-Israeli understanding over closer strategic ties.

Secretary of State Alexander M. Haig, Secretary of Defense Caspar Weinberger and national security adviser Richard Allen individualized the official administration smiles they wore, having accomplished what Allen said was an objective: "to put our bilaterial relationship on a new level."

Sen. Edward M. Kennedy (D-Mass.) smiled too, but with a touch of some old-fashioned partisan reserve. "The prime minister is obviously very heartened by his visit. But I think the new definition of the strategic security relationship has to be spelled out in a somewhat more meaningful form so we'll know whether this is something that has real life to it."

It was an occasion of exquisite planning by Israeli Ambassador and Mrs. Ephraim Evron, whose guests were an impressive cross-section of Washington officialdom, Eastern establishment media and the American Jewish community.

The Evrons, the Bushes and Israeli Foreign Minister Yitzhak Shamir and his wife welcomed everybody in front of the famous Gilbert Stuart portraits of George and Martha Washington. The choice of location did not prove to be a particularly soothing one. The minute Kennedy arrived television lights went on and a gallery official moaned, "My $5 million paintings are melting."

Begin never made it into the receiving line, but sat it out behind closed doors, supposedly on orders from his daughter, Hasia Milo.

"He's very, very tired," said an aide.

"If Mrs. Begin had known his schedule here, I suspect he'd have been ordered to put his feet up even more by his daughter," said Vice President Bush.

After dinner, some guests, such as Joan Mondale and the Moral Majority's Rev. Jerry Falwell and his wife Macel, were welcomed with with hugs or kisses from Begin.

Falwell, who will meet with Begin today, was glowing over yesterday's Senate confirmation testimony of Supreme Court nominee Sandra D. O'Connor. "She opposes abortion, women in combat, and forced busing," he said. "It sounds like she might be able to join the Moral Majority."