Pope John Paul II, at last in the capital of a nation he has touched as few before him, was welcomed to Washington yesterday by pilgrim hymns, sparse crowds, humbled politicians and the autumn splendor of this city.

"You have unleashed the best, most generous sentiments within us." Vice President Mondale told the traveling Pope when he arrived at Andrews Air Force Base for the final two days of his American odyssey. You have given us new hope and new courage. You have graced our nation by your presence, and now you grace our nation's capital."

His white robes billowing in a gentle morning breeze, John Paul made clear his delight at becoming the first pope ever to visit Washington, saying he was "looking forward to meeting the leaders of this young and flourishing country."

But before really beginning the visit that would take him to the White House for a historic personal meeting with President Carter yesterday afternoon and to the Mall for a climactic mass today, the pope -- displaying majestic calm and patience, as always -- decided to linger just a little.

As the Navy Band played "God of Our Fathers," a solemn Protestant hymn, John Paul strolled slowly past the greeting crowd at the airport, now lifting his hands in his inimitable gesture of welcome, now hugging a little girl who had rushed out to embrace him.

From the suburban Maryland air base, the 59-year-old pope was ferried by helicopter to a point near the Reflecting Pool on the Mall where he was greeted by District of Columbia Mayor Marion Barry and members of the City Council before his motorcade traveled up Connecticut Avenue to St. Matthew's Cathedral and from there to a series of encounters with official Washington.

He would up the day with a reception for Washington's diplomatic corps at the Apostolic Delegation.

Earlier, relaxed and smiling, he met with the assembled leadership of the United States and all of the Americans, speaking to them, sometimes admonishing them, in tones both familiar and paternal.

At the White House, after the first of two private meetings with President Carter, the pontiff told gathered members of the Congress, cabinet and the judiciary that he endorsed U.S. efforts to limit the proliferation of nuclear arms. But the pope also called on them to use their influence on other nations "to join in a continuing committment for disarmament."

"Without wholeheartedly accepting such a commitment," said John Paul, "how can any nation effectively serve humanity, whose deepest desire is true peace?"

Elaborating on concerns he has expressed at the United Nations and elsewhere on his tour, the pope pressed for more economic cooperation between rich nations and poor, "even if it involves a notable change in the attitudes and life styles of those blessed with a larger share of the world's goods."

At the Organization of American States, John Paul delivered his most stinging attack to date on the dictatorships of Central and South America. Speaking to the delegates in Spanish, English, French and Portuguese, the Pope dismissed the notion that individual rights may legitimately be subordinated to the security of the state.

"A security in which the peoples no longer feel involved because it no longer protects them in their very humanity," he said, "is only a sham."

Perhaps because official Washington reserved so much of the pope's time yesterday, perhaps because people were waiting to join him on the Mall today, the corwds that greeted John Paul as he rode through the streets of the city were smaller than any he has seen since coming to this country last Monday.

The throng in Lafayette Square, across the street from the White House, numbered only a few thousand. Along the motorcade route up Connecticut Avenue to St. Matthew's Cathedral, the sidewalks were lined no more than five and six deep with people, far short of street crowds in Boston, New York, Philadelphia and Chicago, the other major cities on the pop's tour.

It was only on Rhode Island Avenue outside the cathedral that the pope found an elbow-to-elbow crowd. And it was there, as the noontime sun shone brightly from the deep blue sky overhead, that John Paul had his most emotional encounter with the people of Washington.

On his way to the cathedral, the pope had moved swiftly from his black limousine into the church, so quickly, in fact, that most of the 12,000 people on the street did not even see him.

They waited patiently for the mass inside to finish. Street vendors hawked their wares -- bumper stickers that said "Got a Peek at the Pope," T-shirts, buttons, pennants, calendars, souvenir newspapers -- but most in the crowd seemed uninterested in such things, their attention fixed on getting just a glimpse of the charismatic man who had drawn them there.

Finally, in more of a plea than a demand, they began chanting: "We want the pope. We want the pope. John Paul II, we want you."

And of course, they got him. The balcony door over the cathedral's rectory opened slowly, and out stepped John Paul, his white hair blowing in the breeze. He gestured, tapped the microphone, and responded in a way that at once won over another audience.

"John Paul II," he said. "He wants you. And he will say to the President of the United States [who was to see the pope in the White House shortly] that he comes too late because of you."

Even when he addressed the political elite assembled at the White House a few minutes later, John Paul made it clear that he was interested in them only insofar as they represented the people of America. It was the people, as always, that he really wanted to address.

In the streets of Washington yesterday, it seemed that he had reached them. As they milled about, many among the spectators -- Catholics and non-Catholics alike -- were talking of the messages John Paul brought with him, pondering them, if not always accepting them.

"We need a big change in our lives and in our nation," said Jueldenn Ford, a registered nurse at the National Institute of Health and a black Methodist who stood waiting to see the pope's motorcade. "It's an awful lot to ask of one man, but the pope is a good man to start with.

"We are on a collision course," said Ford. "We need to get back to the church and family and things that are basic and good for the world. The pope went to Harlem -- no one goes to Harlem -- and he went to the country folk in Iowa. I thought it was wonderful. If we'd all follow him and do our part, who knows? This might be a different world."

Barbara Kaye, an administrative consultant, noted that her Dupont Circle neighbors were at first cynical about the pope's visit to Washington. "It was 'Oh, yeah, the pope's coming. We better get out of town that weekend.'"

But as the week wore on and they watched John Paul in television and read about him in the newspapers, she said, those formerly cynical upwardly mobile Washingtonians began to make plans to watch the pope through neighbors' windows.

"It's tradition for us in Washington not to be impressed," laughed Kaye. "He's totally conscious of what he represents, but he can make that distinction between rank and man."

After a week of strict preachings from the pulpit from this pope -- preachings against birth control, abortion, divorce, married priests and women priests -- it was inevitable that some in this country of less conservative values would protest what the pope represents. And, indeed, there were demonstrators on the streets of Washington wherever the pope went yesterday.

These protesters were unusually quiet for the most part, however, choosing to make their points simply with the words painted on their large white banners.

The only untoward incident of the pope's first day in Washington occurred at Lafayette Square before the pope arrived at the White House.

At about 1:05 p .m., U.S. Park Police arrested a man who was seen carrying two huns under his jacket. Police said before the arrest, the man, who was leading a large dog by a leash, had demanded to see Carter. Timothy R. Burgess, 36, of Miami, Fla., was charged with carrying dangerous weapons.

But most of those who lined the pope's path through Washington yesterday were the faithful, and more than a few were pilgrims.

As early as Firday, clusters of people had begun setting up camp on the mall, which by 3 this afternoon may be filled with one million of the faithful and the curious. While John Paul moved through the streets and centers of power yesterday, workmen were still putting the finishing touches on the altar.

Testing, testing, testing. . .boomed a voice across the Mall, the sound echoing off the granite monuments nearby.

But for this city and Pope John Paul II, the extraordinary Catholic figure who has seen more millions of Americans in one week than any man in history, the final joyous test of his seven-day pastoral visit to the United States comes today.