The Mystery of Romance?; The Black Seraphim, by Michael Gilbert. New York: Harper & Row. 216 pp. $13.95. A Death at St. Anselm's, by Isabelle Holland. Garden City, N.Y.: Doubleday & Co. , Inc. 229 pp. $13.95.

Romance is popping up everywhere these days, even in murder mystery novels. The romantic possibilities in most murder mysteries are usually repressed in order to keep these novels within the confines of the genre. Romance can get out of hand and could so easily detract from the mystery. And, after all, the main point of a murder mystery novel is the mystery.

Two recently published murder mysteries share a background of Anglican church politics. They also emphasize romance and thus run the risk of failing as murder mysteries. ''A Death at St. Anselm's,'' by Isabelle Holland, comes close to failing; ''The Black Seraphim,'' by Michael Gilbert, succeeds spectacularly. The romance in ''The Black Seraphim,'' like every other aspect of this mystery novel , fits neatly into the pattern of the story. The romance in ''A Death at St. Anselm's'' threatens to take over the story and almost turns this mystery into a romantic suspense novel.

The plot of ''A Death at St. Anselm's'' is weighted more toward the romantic than the whodunit. When Dick Grism, business manager of St. Anselm's Episcopal Church on New York's Park Avenue and East Sixty-second Street, is murdered, the Rev. Claire Aldington becomes a suspect. She also finds herself revising her previously low opinion of banker Brett Cunningham, St. Anselm's former business manager. Claire and Brett have battled in the past over the allocation of church funds. The murder investigation brings them together, and love blossoms.

I was more curious to find out how their relationship would progress than I was to find out the identity and the motive of Dick Grism's murderer. The romance in ''A Death at St. Anselm's stole the show, further weakening this already mediocre mystery novel. At the same time, the romance provided a diversion.

In ''The Black Seraphim,'' on the other hand, the romance is one of several elements that combine to make it an excellent mystery novel. ''The Black Seraphim'' has good writing, interesting characters, a suspenseful plot, subtle humor, and a romance that, although secondary to the mystery, serves to complicate the plot and intensify the suspense.

When Dr. James Scotland, a young pathologist from London, visits the cathedral town of Melchester, he finds himself embroiled in a complicated town vs. gown conflict that results in the murder of the archdeacon. Archdeacon Pawle wanted to sell some of the cathedral's land to a shady land development company backed by some powerful and dishonest local figures. Opposing the scheme is the dean of the cathedral, Dean Forrest. His daughter, Amanda, and James Scotland fall in love. When James pursues his suspicions about the cause of the archdeacon's death, Amanda and her father become suspects in the murder case, and Amanda severs her relationship with James. Everything gets straightened out in the end, but not before there are several more plot twists.