What is usually called the Gay Agenda actually existed in two articles by Marshall K. Kirk and Erastes Pill, called "Waging Peace." The first part appeared in Christopher Street Magazine (a gay literary magazine in New York) and the second part in The Guide (a gay travel magazine based in Boston). Unfortunately, all the copies I can find online are seriously marked up by right-wing, homophobic publications.
It was a plan to transform the wild-in-the-streets, rag-tag, Gay Liberation movement into a respectable civil rights organization. Naturally, it did not entirely sit well with old Liberation types like me (see source).
Basically it said, cut your hair, put on a suit and tie instead of tie-dyed T-shirt, do not be outrageous, do not demand "gay" as a right that everyone is entitled to if they wish, but portray it more or less as a genetic condition which people are helpless to change, plead for concessions in gay rights by appealing to compassion, sort of like ramps for people who are wheelchair bound. (This is my critical view.)
The point which most infuriated the right wing and religious homophobes saems to be the claim that sexuality is immutable. Yet this seems to be entirely true. If it isn't, no one has found a way to disprove it. They claimed it was a plan to turn children gay, which of course would be impossible if sexuality is immutable. What neither side ever seemed to consider was that there is a right to be gay, however people arrive at being gay.