West Germany's foreign minister, who visited Egypt's Vice President Hosni Mubarak in Cairo last night, said today he was impressed by the "confidence and determination" Mubarak showed in preparing to step into the place of Anwar Sadat.

At the same time, Bonn's Hans-Dietrich Genscher signalled his government will continue to press for a widening of the Israeli-Egyptian peace process and the realization of the right for Palestinian self-determination.

Genscher, who has had several meetings with Mubarak over the years, was the first senior Western politician since the assassination Tuesday to see the man the Egyptian parliament named to succeed Sadat. Genscher stopped in Cairo at Mubarak's invitation while returning from an official visit to China.

The midnight meeting lasted an hour, just long enough, according to participants, for the West Germans to get a general, firsthand impression of Egypt's future leader.

"What is impressive is the confidence and determination with which he is tackling his duty," Genscher said of Mubarak. "He left us with the impression that the situation in Egypt is stable, and what is particularly important, that Egypt will consequently continue president Sadat's foreign policies."

Mubarak's quick nomination by the parliament, Genscher said, showed that "he can count on a strong basis of trust."

"One should know that he already participated considerably during the last few years in formulating Egyptian policies, and that since he comes from the Army, he has a strong position" there as well, the minister said.

In two radio interviews today, Genscher also directed some remarks to Israel, stressing that the Jewish state needs to show a "constructive attitude" in coming negotiations on Palestinian autonomy in order to help Egypt's new leadership carry through its intended policy.

West European leaders have been pushing formally for full self-determination for the Palestinians since they signed a resolution to that effect in June 1980. Israel has long been urging friendly governments to refrain from using the term self-determination, which Arab leaders tend to equate with the possible formation of an independent Palestinian state.

Voicing doubts as well about progress on the Palestinian problem through talks that are limited to Israel and Egypt, European leaders have called for the involvement of the Palestine Liberation Organization in the peace process -- over Israeli and American objections.

But in view of Mubarak's stated commitment to follow through on the 1979 Israeli-Egyptian Camp David peace accords, Bonn officials do not expect that the process can be widened to include others until Israel withdraws from the last third of the Sinai, which is scheduled to take place next April.

For now, Genscher urged countries that have friendly ties with Egypt to make clear their political backing of Cairo's new leadership.

"Recognition and support from the outside will make the task of the new leadership easier during a period of change that will not be easy," he said.

In addition, Genscher stressed the importance of Egypt solving its economic problems, but Bonn officials traveling with Genscher said that the subject of extra West German aid was not brought up.