President Reagan, in a move that appeared to mark at least a temporary end to a five-month struggle between Secretary of State George P. Shultz and Republican conservatives, yesterday nominated Rozanne L. Ridgway, the U.S. ambassador to East Germany, to be assistant secretary of state for European and Canadian affairs.

If confirmed by the Senate, Ridgway's appointment would mark a major victory for Shultz. He chose the career diplomat for the post despite protests from conservatives that he has been conducting an "ideological purge" designed to give him control over the administration's foreign policy machinery.

Ridgway would succeed Richard R. Burt, whom Shultz has recommended for ambassador to West Germany. Burt also has been a target of conservatives, who say he is more representative of the so-called "foreign policy elitist establishment" than of Reagan's hard-line views, but administration sources said the president is expected to announce Burt's nomination for the Bonn embassy "within a matter of days."

The unhappiness of conservatives over what they believe is Shultz's desire to freeze them out of the policy-making process surfaced late last year and contributed to unusually long delays in filling several key diplomatic posts.

In some cases, the considerable paper work accompanying nominations caused delays. But a number were held up at the White House while such influential conservatives as Sen. Jesse Helms (R-N.C.) and Rep. Jack Kemp (R-N.Y.) fought a stubborn rear-guard action aimed at persuading Reagan that Shultz's choices were unsatisfactory.

In an effort to pacify the conservatives, Shultz found new posts for some of the conservative-backed officials he had marked for replacement at the State Department.

These include Richard T. McCormack, who will shift from assistant secretary for economic affairs to ambassador to the Organization of American States; J. William Middendorf II, who moves from the OAS to become ambassador to the European Economic Community, and Lewis A. Tambs, who will leave the embassy in Colombia to become ambassador to Costa Rica.

For the most part, however, Shultz refused to bow to conservative efforts to trim the number of career foreign service officers he had recommended for ambassadorships. He also strongly resisted moves to derail his choices for several especially sensitive posts -- including Ridgway; Burt; Winston Lord, who is to become ambassador to China; Thomas R. Pickering, who is to move from El Salvador to Israel, and Harry G. Barnes Jr., set to become ambassador to Chile.

Shultz's persistence eventually paid off. Recently, a deluge of Shultz-sponsored nominations has poured out of the White House, confronting the Senate Foreign Relations Committee with the prospect of holding at least 20 nomination hearings by June 20.

Nominations already scheduled for hearings include those of Middendorf, Tambs, McCormack, Pickering, Barnes, Nicholas Ruave (ambassador to Iceland), John Scanlon (Yugoslavia), John Fertch (Honduras), Charles A. Gillespie Jr. (Colombia), Lowell C. Kilday (Dominican Republic), Sheldon J. Krys (Trinidad), Fernando E. Rondon (Ecuador), Edward M. Rowell (Bolivia), Peter Bridges (Somalia), Edward J. Perkins (Liberia), Lannon Walker (Senegal), Robert Pugh (Mauritania), Paul Hare (Zambia) and David Newton (Iraq).