President Carter wound up two days of intensive foreign policy activity here today, but he also toured a decaying section of the South Bronx to symbolize his concern for the purely domestic problems that plague American cities.

The President signed two UN documents pledging the United States to uphold its citizens' human rights, and throughout the day he met with scores of foreign officials at luncheons, receptions and private meetings.

But all this came only after Carter slipped out of the U.N. Plaza Hotel this morning and, with New York Mayor Abraham Beame and Housing and Urban Development Secretary Patricia Harris, drove to the Bronx, winding through aging neighborhoods near Yankee Stadium.

White House officials kept the plans for the tour secret to prevent the usual herd of reporters and photographers from accompanying the President. They said he wanted to see the area with a minimum of disruption.

As a result, the people of the South Bronx could not have been more surprised as they spotted Carter's tan limousine on their streets, its U.S. and presidential flags flapping in the breeze.

On one street, Carter passed two men who sat drinking beer from cans in paper bags.Small groups of startled spectators spotted him, shouting out "Send us money" and "We want jobs."

At one point, the President got out of his car and walked for about a block, chatting briefly at the door of one renovated building with the executive director of a neighborhood redevelopment agency.

Since taking office, Carter has been criticized for giving a low priority to urban problems, particularly in the big cities such as New York. His 75-minute tour today was clearly meant to soften such criticism.

Following the tour, Beame disclosed that the President had asked him to become chairman of the Commission on Intergovernmental Relations and that he is seriously considering accepting the non-salaried, advisory post. Beame lost his Democratic primary bid to win re-election and will leave office Jan. 1.

The documents the President signed here today were the United Nations' International Covenant on Economic, Social and Cultural Rights, and its International Covenant on Civil and Political Rights. Both must be approved by the Senate before they take effect.

The covenant on economic, social and cultural rights pledges a nation to recognize its citizens' rights to work, fair wages, social security, adequate standards of living and freedom from hunger, and to health and education. It also guarantees the right to form and join trade unions.

The covenant on civil and political rights prohibits slavery, guarantees the right to a fair trial and to protection againt arbitrary arrest or detention. It also recognizes freedom of thought, conscience, religion and expression, the right of peaceful assembly and emigration and freedom of association.

The United Nations adopted the documents in 1966, but they did not take effect until 10 years later when the required 35 nations had ratified them.

At a luncheon with Asian foreign ministers, Carter noted that "a few of you are nations where we don't yet enjoy full diplomatic relations." That is true of China, North Korea and Vietnam, and the President added:

"We would like to establish those diplomatic exchanges with you without delay so that we might proceed to alleviate the differences that divide us and also assess and take advantage of the common problems that we can address together."

Carter has packed an extraordinary amount of activity into these two days, seeking to see officials from every corner of the globe. Today, for example, in addition to the lunch with the Asian foreign ministers, he was host at a reception for Latin American foreign ministers, met with U.N. Secretary General Kurt Waldheim and his staff and conferred privately with the foreign ministers of Lebanon and Poland and with President Spyros Kyprianov of Cyprus. He also met early tonight with New York Gov. Hugh Carey.

The President returned to Washington tonight.