* Some 4 million adults enrolled in correspondence courses in 1973. Nearly 2 million of them were under the aegis of the military, and 1,062,749 in National Home Study Council member schools.
* Community organizations in 1972 such as churches, YMCAs, the Red Cross, and social service groups counted 10,968,000 participants in locally sponsored adult education programs.
* Post-secondary institutions such as vocational schools, two-year colleges, and four-year degree-granting colleges and universities enrolled 7,416,000 adults in 1975.
* It is estimated that in 1982, as in 1981, more than 20 million adults will be going to school via the mailbox, the TV, the local public school, the street-car college downtown, the classroom in the plant, or even the college campus.
A helpful book for those just starting their search for an institution (a degree-granting college or university) that is prepared to take adult scholars is now available from Peterson's Guides Inc., PO Box 2123, Princeton, N.J. 08540 ($6.95).
The title: ''Who Offers Part-Time Degree Programs?''
Those interested in the whole business of adult education - but not in comsumer information of where to go - might enjoy Paul Barton's excellent study of what he titles, ''Worklife Transitions: The Adult Learning Connection.'' (New York: McGraw-Hill. $14.95)
It's chock-full of statistics, like those noted above, but not overwhelmed with them.
To underline the trend toward more offerings for adults in further education, a news release from Yale University (dated Dec. 16, 1981) states:
''For the first time in its history, Yale has established an undergraduate program for nonresident, older special students, who will have up to seven years to complete requirements for the new bachelor's degree.''
The release continues, ''These special students . . . can register for the same college courses taken by Yale undergraduates and will be subject to the same high academic standards.''
It's an amazing phenomenon, and a continuously growing one: Those who want to learn more may do so, pretty much at their convenience. Yale is not the first of the highly selective liberal arts colleges to accommodate the adult student, nor the last.