It is an irony of scheduling that the first major speech of the 1980 Republican convention will be given by the GOP leader who may be furthest from the center of this conservative-dominated conclave.

Michigan Gov. William G. Milliken, who will welcome the delgates Monday evening, lobbied long and hard to bring the convention to Detroit. In an interview Saturday, he said, "The presence of the convention gives us a major lift when our fortunes are in the depths -- when our unemployment rate is the highest in the country and the problems of our minority youths are beyond description."

But as hard Milliken worked to bring the convention to Detroit, he worked equally hard to keep Ronald Reagan from being its nominee. In May, the boyish-looking 58-year-old blueblood put all the political chips he had accumulated in almost 12 years as governor on the line for George Bush.

With Milliken's muscle, Bush gave Reagan his worst primary beating of the year -- a 2-to-1 defeat -- in the May 20 primary. But it was too late to halt the inevitable.

A Yale-educated department store heir from Traverse City, Milliken comes before the convention as the most visible and effective survivor of the moderate-liberal establishment that dominated the national Republican Party until Barry Goldwater's nomination in 1964 and the emergence that same year of Reagan as a powerful conservative spokesman.

Unlike most of the other GOP progressives, Milliken has not accepted defeat with a shrug of resignation. His role here has been and remains that of an in-house critic of the ruling Reaganism -- not bolting but not bending his convictions, either.

A week ago, Milliken told the platform committee he thought it "imperative" that the GOP reaffirm its support forthe Equal Rights Amendment. In an interview he said its rejection by the platform committee was "a mistake, but it's probably not an issue that will in and of itself determine the outcome of the election."

Still, he said, "it's extremely important" to many people and "Reagan would be well advised to address the question of equal rights in his acceptance speech."

Milliken's outspoken wife, Helen, said she thought a rhetorical bow from Reagan would be an empty gesture at this point, because "what counts is the amendment, not all the fluff they put inthere in the plank" on women's rights. On Monday, Helen Milliken and at least three of Milliken's top staff aides will be in an ERA march -- and the governor may be with them.

On another issue that Reagan has underlined -- turning back programs and tax sources to the states -- Milliken said, "It has some appeal but it depends on how it develops." Reagan always cites welfare as a program that Washington should relinquish, but Milliken said, "Welfare is not the example I would want to bite on. Turning it entirely over to the states would perpetuate the inequities in benefit levels we have now; our best hope is to get welfare reform at the federal level and reduce some of those inequities."

But despite his disagreements, Milliken rejects the option of bolting the GOP to follow his good friend, John B. Anderson, into the independent ranks. Eh said he thinks Reagan can carry Michigan -- particularly if he picks Bush as his running mate. "That," he said, "would indicate Reagan is really ready to make a broad appeal."

Milliken's overriding interest in the last six years of his governorship has been sustaining Detroit, and there he thinks the conservatives have ideas to offer.

"I would like to see Gov. Reagan express in a convincing way hiss understanding and sensitivity to the human impact" of recession and layoffs on city dwellers, Milliken said, "and then follow up with specific programs like Jack Kemp's proposal to give tax incentives to private businesses that take the risks of opening up new plants and jobs in the cities."

Milliken said he admires and supports Reagan's refusal to back import curbs as a quick-fix for the ailing U.S. auto industry. "We have to approach our problems from a different point of view," he said, "and our best hope of doing that is with a Republican administration."

Whether Reagan is the man to lead that change is a question on which Milliken is deliberately withholding judgment.