Popular Civil War saga; North and South, by John Jakes. New York: Harcourt, Brace, Jovanovich. 740 pages. $14.95.

Remember how easy it was to doze off in your American history class? Well, if John Jakes had been the teacher, you wouldn't have!

Mr. Jakes is making history--or at least the historical novel--interesting for millions. ''North and South,'' his first hardcover novel, has quickly taken over the best-seller spot. (His eight-volume Kent Family Chronicles sold over 30 million copies altogether.)

The author knows the rules for a successful generational saga: give the reader just enough history to lend flavor to the story, but let your characters carry the day.

I didn't need to be reminded of how good Mr. Jakes is at his craft. I was hard-pressed to slow down and read the paragraphs of historical insight and speeches which presented the views of both sections of the country. What I really wanted to know was what was going to happen next to Orry, son of a South Carolina plantation owner, and George, son of a Pennsylvania iron maker, and their families. The two young men met as cadets at West Point; and their friendship continues as the country tumbles toward war.

The themes are strictly soap opera: Will Orry get his true love, Madeline, who is presently married to a ''Simon Legree''? Will beautiful Ashton seek revenge on sister Brett and Billy? What side will Orry's brother, a Southerner opposed to slavery, take in the war? And what awful deeds will rabid abolitionist Virgilia commit in the name of liberty?

The diverse characters give us the varying shades of opinion that people, North and South, held on slavery in the two decades before the War Between the States. Mr. Jakes skillfully shows how these feelings could rend the strong ties that bound friends, families, and a country.

John Jakes doesn't give us memorable passages. But he does give us an engrossing tale that keeps us reading for 740 pages, and waiting anxiously for part two of this trilogy.