Ronald Reagan tends to be more optimistic about the Republican presidential nomination after his occasional losses in the GOP primaries than after his many victories.

Tonight was no exception, as Reagan issued a statement following his defeat in Michigan saying that "the future looks very good."

Including his expected win today in Oregon and his loss in Michigan, Reagan has now won 17 of the 21 primaries in which he has completed with George Bush. Reagan's official count showed him with 863 of the 998 delegates needed for nomination entering today's primaries, and his strategists predict he will now clinch the nomination in next week's primaries in Idaho, Kentucky and Nevada.

"We've made a step forward tonight toward the nomination," Reagan said in a statement issued through a spokesman here. "Based on the officially selected delegates, we don't have the number needed for nomination. But today's results move us to that goal and, based on reasonable projections, we're very optimistic. The future looks very good."

For the first time during the campaign, Reagan spent a primary day at his ranch near Santa Barbara. Late tonight he came down the mountain from the remote ranch to discuss the primary results briefly with reporters.

Even before the returns came in, Reagan and his strategists had concluded that they would not press Bush to drop out.

Within the Reagan camp, there are those who care less for Republican rival Bush than they do for Jimmy Carter, or maybe even the Ayatollah Khomeini. These Reaganites see Bush as a party wrecker whose persistence in a long-lost cause diminishes the chance for Republican Party unity in November. They would like to criticize their opponent in these terms.

But this is not the prevailing view, perhaps because the candidate will have none of it. While Reagan has been irritated at times with Bush, particularly for his allegation that the Kemp-Roth bill which Reagan espouses would increase inflation by 30 percent, the former California governor refuses to say either publicly or privately that Bush should get out of the race.

Reagan wants Bush out and thinks that his withdrawal would give the Republican campaign an advantage, particularly since Sen. Edward M. Kennedy is persisting in his challenge to President Carter. But Reagan believes it would be counterproductive to put pressure on Bush.

"We want unity and you don't get it by hitting a guy when he's down," a Reagan aide said today. "Bush is really down and he's got nothing going in California to bring him back."

Reagan came into partisan politics in the Barry Goldwater campaign of 1964, when the Republican Party was shattered by deep philosophical and personal divisions. The lesson was not lost on Reagan, who moved quickly to heal ideological wounds after his own victory over a moderate candidate in the 1966 GOP gubernatorial primary in California.

Some say that Reagan also remembers 1976 when the political operatives of then-President Ford tried to force him out of the presidential race after he had lost five straight primaries. And others observed that Reagan is merely recognizing the political reality that Bush will find it tough to stay in after the June 3 round of primaries.

Whether Reagan already has mathematically clinched the nomination is arguable but the candidate and his strategists are convinced there will be no dispute after California's 168 delegates are chosen in its winner-take-all primary on June 3. Reagan holds a 7-to-1 lead over Bush in published polls, and Bush is not even scheduled to return to California campaigning until the middle of next week.

So, the Reagan strategy would make it easy for Bush, if he chooses, to change his mind and pull out of the race gracefully.