Lyndon B. Johnson stood before a vast sea of another President's fellow townspeople last night and told them solemnly that he intends to "carry on the spirit, the ideals and the programs begun by that son of Boston, John Fitzgerald Kennedy."

As he spoke, President Johnson looked out on the Common-wealth's largest political gathering of the 1964 campaign. Police estimated that over 350,000 people lined the route of the Presidential motorcade and packed a climactic outdoor rally in Post Office square.

"He led an entire nation, and found his way to the secret hopes of man," Johnson said of his predecessor. "When he died the sound of mourning was heard in every street of the earth. But tears came more plentifully to Boston eyes, and grief more painfully to Boston hearts."

Johnson said that two of Kennedy's qualities "especially explain his hold on men."

"He made them feel they were better than they had thought they wore: that perhaps, on earth, God's work might truly be their own. And he could absorb, in his imagination, the dreams and longings, the fears and ambitions of others, whether they lived in mud huts in Africa or in the palaces of kings," Johnson said.

Crowd Quiet

Most of Johnson's speech was devoted to a recital of the hopes and accomplishments of President Kennedy. The crowd listened quietly, and there were few of the "punch lines" or cheers that usually mark a political rally.

Johnson praised Kennedy as a man of courage, principle, dedication and judgment.

"We saw that judgment after Cuba," he said. "We did not press our victory or try to humiliate the Soviet Union. Instead we seized the chance to move toward meaningful and lasting settlements which might lessen the danger of war."

Departing from his prepared text, Johnson recalled in somber tones that he had taken the oath of office "11 months and three days ago on that tragic day. November 22, amid the roar of the jet planes" and that he "attempted to pick up where my beloved benefactor and friend had left off."

The President shared the platform with Boston's Mayor John F. Collins, Gov. Peabody, the state's Democratic Congressional delegation, and the local candidates his trip was designed to strengthen.

Bed-ridden Sen. Edward M. Kennedy was represented by his wife, John. When Johnson mounted the platform, he walked straight to Mrs. Kennedy, kissed her on the cheek and grinned as she blushed and the crowd reared with delight.

"I'm not a prophet," the President said, "but in due time Sen. Kennedy will lead a lot more people than those of Massachusetts. He sits there in the Senate and He represents all that's good and all that's beauty and all that represents patience and understanding."

Johnson recommended the election of gubernatorial candidate Francis X. Bellotti and "the straight Democratic ticket from the courthouse to the White House."

Powerful searchlights played on "the tall buildings surrounding Post Office Square and hundreds of policeman ringed the crowd.

The President was hoarse and apparently tired at first, but he grow relaxed and expensive as he spoke. After his speech he leaned over the platform and shook perhaps 154 hands in about two minutes.

The Presidential jet, embiazoned with the words "United States of America," touched down at Logan Airport at 5 p.m., a half-hour behind schedule. It took off again at 6:40.

In the motoreads, which toured the main thoroughfaros downtown past cheering crowds five and six deep, Johnson rode in the Lincoln limousine in which his predecessor was assesinated. The car has been completely rebuilt and a bulletproof plastic top was added.

Many people at the rally waved "Hello LBJ" pennants and Bellotti-for-Governor posters. A few Goldwater signs were seen, and four placards protested the proposed closing of the Watertown Arsenal