The only thing missing was the cherry pie. But there was plenty of American patriotism in store yesterday for Canadian Prime Minister Pierre Elliott Trudeau and Mrs. Trudeau, the second state visitors of Jimmy Carter's month-old presidency.

The Trudeaus arrived in mid-afternoon, one week to the day after Mexican President and Mrs. Lopez Portillo paid their respects to the new administration. The Trudeaus' visit coincided with the official observation of George Washington's birthday, which provided a patriotic theme for entertainment at last night's State Dinner.

The White House had chosen a musical retrospective of 200 years of American history, performed by a group of 19 theatrical students from Columbia, Md. In keeping with the low-key no-frills focus established at the Lopez Portillo dinner, White House chefs prepared a basically American menu of Alaskan crab and roast crown of lamb.

The two-day visit of the Trudeaus, which will include the first address ever by a Canadian prime minister to the U.S. Congress, has been called "a very critical" one by the Canadians. At the arrival ceremony on the White House South Lawn, throngs of Canadians and Americans cheered loudly and waved the flags of both countries.

Watching from the vantage point of the stairs leading to the Truman balcony were President and Mrs. Carter's family and closest aides, including 9-year-old Amy Carter wearing two miniature flags representing each nation in her green cap.

The informal style thus far adopted by the Carter administration for official events and the patriotic theme selected for last night's dinner seemed to agree with the visitors.

Trudeau bounded out of a limousine in a well-traveled trench coat with a yellow rosebud pinned to the lapel. Mrs. Trudeau, who has defended her dressing habits (including a love of blue jeans) on Canadian national radio, was elegantly attired in a white fox-trimmed powder-blue coat with a matching fox hat. She was met by Rosalynn Carter -- wearing a white wool coat over a red dress -- who handed her visitor a large bouquet of red roses.

Despite the relaxed air of the welcome (no "Ruffles and Flourishes" or "Hail to the Chief," but a 19-gun salute) the White House had issued a program carefully outlining "customs." The instructions read: "During the playing of National Anthems, salute by placing your right hand over the heart. If gentlemen's hats are worn, the hat is held over the left shoulder with the hand over the heart."

Vice President Walter Mondale, hat-less as were most of the civilians present, held the lapel of his overcoat during the anthems. Acting Secretary of State Warren Christopher, representing Cyrus Vance who was due back last night from his mid-east mission, held his hand firmly over his heart.

In their brief messages, both Carter and Trudeau issued strong praise for each other's countries and the historic relationship between them. "We share a common border of 5,000 miles . . . a common defense . . . human and natural resources of an entire continent," said Carter, calling Canada "our most important trade partner."

Trudeau complimented Carter's "dedication . . . hard work . . . sense of morality," thanked him for being invited "early" and spoke of "great expectations that this continental neighborhood will flourish."

"Perhaps there's nothing our countries can do that does not involve one another," said the 57-year-old Trudeau, Canada's prime minister since 1969.

There was general laughter when he alluded to a prior meeting of Rosalynn Carter and Margaret Trudeau, two weeks ago in Washington. They "established a good agenda for our discussion," he said. "We (he and Carter) are only meeting at this moment."

A morning rehearsal by the group known as the Young Columbians provided a preview for reporters of the 30-minute revue the Carters' guests would see following last night's dinner. The revue was originally prepared for the Bicentennial, and the group danced and sang to American music spanning this country's 200 years.

Starting with colonial times and the American Revolution, selections proceeded through six other wars in which Americans fought. The Vietnam war never was mentioned by name but such songs as "Where Have All the Flowers Gone" left little doubt of its significance to the young performers.

White House social secretary Gretchen Poston, quickly becoming the Carters' chief talent scout for entertainment, said the program was exactly what the Carters wanted.

"There's a time for Serkin (the world-renowned pianist who performed for the Lopez Portillo dinner) and a time for this. Mrs. Carter and I talked about the talent. And this is a young, vibrant program that is apprepriate for the Trudeaus."

"It couldn't be a better birthday for George," she added.