White House conferences, according to the conventional wisdom, have all the relevance and immediacy of a Sunday morning sermon on the wages of sin.

Delegates come from all over the country, talk endlessly, pass resolutions on hundreds of arcane and bizarre subjects and then go home, leaving the world much the same as it was before--save that the federal government is several million dollars poorer for the experience. That is the conventional wisdom shaping expectations for the recommendations of the third decennial White House Conference on Aging, which concluded here last week.

A closer examination, however, reveals that White House conferences concerned with aging have not been exercises in irrelevance and futility.

After a great deal of discussion and controversy at the first conference in 1961, which produced roughly 700 resolutions, a key committtee approved one calling for the funding of a nearly universal health insurance plan for the elderly through the Social Security system. That program came to be known as Medicare.

The 1971 conference produced about 660 resolutions, including a call for federal regulation and insurance of private pension plans--an idea that was embodied in the Employe Retirement Income Security Act of 1974.

Considering that 600 resolutions were adopted at the conference that concluded last week, it seems reasonable to predict that many will disappear into that special limbo reserved for the reports and official suggestions of governmental committees, commissions and conferences. On the other hand, considering the political force that older Americans are beginning to represent and the surprising degree of consensus that existed, it also seems reasonable to predict that some of the conference's more salient proposals will find their way into the statute books before the decade is over.

Some other resolutions passed at the 1961 and 1971 conferences called for:

Adjustment of Social Security payments to fluctuations in the cost-of-living index.

Increased appropriations for the elderly under public assistance programs.

Establishment of a House Select Committee on Aging.

Better urban and rural transportation for the elderly.

All of these resolutions have become a reality. Even if they might have been realized without the nudge provided by conference sponsorship, the conferences--at least as far as the elderly are concerned--have served another function.

The 1981 conference was a major political event for the Reagan administration, and not an entirely successful one. In the 20 years since the first conference, the United States has begun experiencing profound economic, demographic and social changes. It is growing older.

For the first time, Americans older than 60 outnumbered those under 10 and those between 11 and 19. In the next 55 years, the general population is expected to grow by 35 percent, but the number of persons 65 and older will more than double, and the number 85 and older will more than triple.

A new militancy is replacing the stereotyped image of older Americans, smiling benignly in their rocking chairs, a shawl over their shoulders. At one point in the conference, while demonstrating against action taken by the key committee dealing with Social Security, several hundred elderly delegates and observers broke into "We Shall Overcome."

Organizations representing the elderly now have political clout. The American Association of Retired Persons and the National Retired Teacher Association claim a combined membership of more than 13 million. The AARP/NRTA constitutes, in numbers at least, the backbone of the Leadership Council of Aging Organizations, the umbrella group that represents more than a score of advocacy groups. The council claims to speak for more than 16 million persons.

The council put its considerable organizational skills behind a traditional social welfare program of increased benefits and protection for older Americans, including passage of a national health insurance plan. The nearest this White House conference came to supporting national health insurance was a vaguely worded proposal to support "continuation of the search for a national health care security plan."

The 1981 conference was the first conducted in the highly charged atmosphere of political confrontation over issues at the top of the legislative agenda. Although conflicting resolutions were passed concerning the use of general revenue funds to support Social Security--1971's conference took a clear position in favor of such support--the conference opposed any further reduction in benefits to current Social Security beneficiaries, called for restoration of the minimum benefit eliminated by the Reagan administration, and urged maintenance of current benefit levels for future recipients. These are all front-burner issues for the administration and Congress.