ABIDJAN, Ivory Coast (AP) _ U.S. Treasury Secretary Robert Rubin told African banking officials Monday that private investment was the key to fostering growth across the continent.

Rubin's week-long trip to four African nations follows President Clinton's visit in March and April to the region to make a strong push to boost economic development across the continent.

Rubin told African Development Bank officials that investors have begun to to take a new look at African nations after decades of ignoring the continent. But he said those countries still face difficult challenges.

Among other things, African countries must implement policies to create political and social stability, a sound legal framework and openness to international trade and investment.

``We can't and you in Africa can't turn away from these difficult political challenges,'' he said.

Investment in sub-Saharan Africa remains pitifully low, Rubin noted in his speech, attracting just 3 percent of total long-term private capital investment to developing countries in 1997. In addition, many countries are heavily dependent on donor aid and loans.

He acknowledged that there was a ``perception gap' in how African investment opportunities were seen by the rest of the world, but said there had also been ``a wide array of real problems _ many grounded in Africa's history _ and too little African focus, prior to recent years, on creating an environment to attract private investment.''

Rubin, who leaves Ivory Coast on Monday for South Africa, is also going to Namibia, Mozambique and Kenya.