Citing new revelation from God, the president of the Mormon Church decreed yesterday that for the first time black males could fully participate in church rites.

The dropping of a 148-year-old policy of racial discrimination was made known in a letter from President Spencer W. Kimball to regional and local leaders of the 2.8-million-member church.

Within the Church of Jesus Christ of Latter-day Saints, as it is properly known, membership is open to all races.

Heretofore, however, blacks have been barred from the priesthood, normally attained by white boys at the age of 12.

While Mormons have no paid clergy -- even their bishops are volunteers -- the priesthood is for males the prerequisite to a meaningful role in the life of the economically and politically powerful church. Perhaps more important for devout Mormons, it is required for participation in temple rites which, Mormons believe, assure one of happiness throughout eternity.

The letter to church leaders from the 83-year-old Kimball, which was released to the public from church headquarters in Salt Lake City yesterday, assets that the new revelation came to him after extensive prayer.

"Aware of the promises made by the prophets and presidents of the church who have preceded us that at some time, in God's eternal plan, all of our brethren who are worthy may receive the priesthood, and witnessing the faithfulness of those from whom the priesthood has been withheld, we have pleaded long and earnestly in behalf of these, our faithful brethren, spending many hours in the upper room of the [Salt Lake City] temple, supplicating the Lord for divine guidance," the letter states.

God, the letter continued, "has heard our prayers> and by revelation has confirmed that the long-promised day has come when every faithful, worthy man in the church may receive the holy priesthood, with power to exercise its divine authority, and enjoy with his loved ones every blessing that flows therefrom, including the blessings, of the temple."

A spokesman said the church has "no idea" how many blacks are members, since church records do not indicate race. "But as you can imagine, there are relatively few," said Don Lefevre, of the Salt Lake City communication staff.

Monroe Fleming, 78, a black convert in Salt Lake City who has endured taunts of "Uncle Tom" for his 25 years of fidelity to the Mormon Church despite his inferior status, estimated that there are "fewer than 1,000" black members worldwide.

In recent years the church has been under massive social -- and some legal -- pressures to drop its policy of racial discrimination, which has been an embarrassment to some of its members. For former Michigan governor George Romney, for example, the racial policy impeded his presidential hopes.

Lefevre acknowledged that from time to time individuals, usually disaffected former members, "have filed harassment suits" challenging the church's racial bar "is a matter theology and not a matter for the courts."

Mormon spokesmen declined to specualte on the theological questions posed yesterday.

Does the new "revelation" reported by Kimball mean that God has changed His mind?

Or does it suggest that previous leaders of the church may have misinterpreted "God's will"?

"The Lord has many ways of expressing His will; the mechanics of it I don't know," was all that communication aide Jerry Cahill would say.

Cahill said he had spent most of yesterday answering calls from members of the church "all over the country," seeking to confirm media reports of the change in racial policy. "The ones I talked to were universally pleased," he said. "Many expressed surprise that it happened in their life-time."

In recent years, the Church of Jesus Christ of Latter-day Saints has been one of the country's fastest growing religious bodies. An aggressive missionary program both in this country and abroad -- though not in Africa -- brought 170,000 converts last year, Lefevre said. He said the world-wide membership is close to 4 million.

Every local congregation weaves a tight fabric of the lives of its members with carefully structured activities for men, women and children for each day of the week.For the young men past the age of 12, the ability to play their expected part in the church hinges on acceptance into the priest-hood.

Mormons believe that the greatest happiness in the life after death goes to those who have married, not just in the conventional sense, but who have gone through a special rite in the church's temples marriage "for time and eternity." Only men who are priests in good standing can have such a marriage.

At age 17 or 18, youths are encouraged to give two years to the church as missionaries. Cahill said that with yesterday's change in racial policy, he expected that the church would soon open mission work in Africa, the only continent on which Mormons are not now found insubstantial numbers.