The United States and Angola have moved into a "crucial phase" of talks on the withdrawal of Cuban troops from Angola that could pave the way for elections later this year to launch the independence of Namibia, West German diplomats reported today.

[The reports follow a recent increase in activity in the negotiations with Angola to end South African control of Namibia, a mineral-rich territory also known as South-West Africa. But U.S. officials in Washington said there is no confirmation from Angola that an agreement has been concluded. The Washington sources pointed out that the talks over the Cuban forces have been in a very sensitive stage for several months.]

The issue here has generated a heated controversy within the center-right coalition since shortly after Chancellor Helmut Kohl was elected March 6. But the recent activity has helped to silence some of the criticism, according to West German sources.

Franz Josef Strauss, who heads the Christian Social Union, the Bavarian sister party of Kohl's Christian Democratic Union, has demanded that Bonn sever all contacts with the South-West Africa People's Organization (SWAPO), the rebel group seeking independence, because of its guerrilla activities and the alleged Marxist leanings of its leader, Sam Nujoma.

Strauss insisted that West Germany should improve relations with South Africa by reopening its consulate in Windhoek, the Namibian capital, and voicing support for South Africa's efforts to thwart perceived Soviet ambitions in the region.

But Kohl shunned such advice and aligned himself with the more liberal foreign policy views of his foreign minister, Hans-Dietrich Genscher, who is the leader of the centrist Free Democratic Party.

West German diplomats, who declined to be identified, said today that the talks have reached a very delicate stage and that the United States has divulged only sketchy details to its allies in the Contact Group, which also includes France, Britain and Canada.

Foreign ministers of the Contact Group have met twice in the past two weeks, first at the Williamsburg economic summit and then at a North Atlantic Treaty Organization session Wednesday in Paris. Secretary of State George P. Shultz reportedly told the ministers that the chances for a breakthrough are now much improved and the talks have now reached a decisive stage.

Angola's president, Jose Eduardo dos Santos, also recently visited Moscow, and observers believe that the Namibia talks were discussed.

West German Foreign Minister Genscher and U.N. Secretary General Javier Perez de Cuellar, who met today here, have both taken a keen interest in reviving hopes for an independent Namibia.

In recent months, chances for a Namibian settlement seemed to fade and the Contact Group nearly collapsed. France threatened to pull out of the group, and the talks appeared at a stalemate over the insistence by the United States and South Africa that the Cubans must be withdrawn from Angola before Namibia is given its independence.

The Reagan administration harbors grave suspicions about Angola's ties with the Soviet Union and has shown concern that an independent Namibia could fall under Soviet influence. Angola has insisted that the Cubans are necessary for its defense and the issue should not be included in the talks.