The United States and the People's Republic of the Congo have agreed to normalize diplomatic relations after a 12-year suspension.

The agreement was reached at a meeting in Bonn, West Germany, yesterday between U.S. Assistant Secretary of State for African Affairs William Schaufele and the Congo's foreign minister, Theophile Obenga.

The U.S. reconciliation with the tiny Congo is the latest demonistration of the Carter administration's proclaimed policy of seeking greater contact with all nations. A year ago, the Congo was providing important support to Soviet efforts to supply the Angola forces opposed by the United States.

Word of the informal understanding between the goverments slipped out when Congolese officials mentioned the successful negotiations at a luncheon given for Obenga by West German officials.

The Congo officials did not realize that reporters were attending the luncheon, according to an informal source.

A formal announcement is expected in the relatively near future by both governments. A second meeting between Schaufele and Obenga is not likely to be necessary, sources said.

The United States closed its embassy in the Congo capital Brazzaville in August 1965 after the ruling party's youth movement harassed U.S. diplomats with behavior similar to that of the Red Guards during China's Cultural Revolution.

The Congo, a former French Colony to the northwest of the far larger former Belgian Congo now named Zaire, withdrew its diplomats from Washington shortly afterward.

"There weren't many outstanding problems," one official source said yesterday in explanation of the speed with which Schaufele and Obenga repaired relations in one session.

Brazzaville proclaimed itself a Marxist government after the overthrow of its first president, Abbe Fulbert Youlou in 1963.

Last April, however, the constiution was abolished and full powers were given to a military committee that chose Col. Yhombi Opango, 38, as the nation's new president.

Opango's appointment was viewed as an opening to improvements in the Congo's relations with Western powers. He was educated in France and has strong ties to the military there. Opango succeeded Marien Ngouabi, who was assassinated in March.

During the Angolan civil war that followed Porgual's decision to give its former African colony independence, the Congo port Pointe-Noire became a major off-loading place for Soviet ships carrying military supplies to the ultimately victorious Popular Movement for the Liberation of Angola.

The United States aided other factions in the civil war.

Brazzaville's role in the Angola civil war is "a little bit of water under the dam now," one source said.

The major questions that had to be resolved concerned U.S. desires to avoid a reptition of the harassment of diplomats encountered in 1965 and the former U.S. properties nationalized the Congo.