Spot cable advertising jumped 26% over last year to $ 31.2 million for first quarter ’93, according to a new industry analysis released Tuesday by Cable Networks Inc.CNI also projects that second-quarter spot will soar by 67% to $ 30.6 million from $ 18.3 million in 1992. The first-quarter growth was sparked by the largest category, automotive buys — especially Ford and Dodge — which were 32% above 1992. Spot buying from dining and drinking establishments, which was the second-largest spending category, was up 16%. The two categories that showed the sharpest declines were retail apparel stores (down 57%) and telecommunications (down 68%). CNI is projecting the spending from the automotive and dining/drinking categories to continue in second quarter, with increased spending by the amusement/recreation category and hotel/motel category.