Dick Van Dyke, dressed as a priest, was making a confession:

"When Stanley Kramer asked me to play this part, I said to him, "You must be crazy. This is serious stuff and I'm a comedian."

But Kramer believed in Van Dyke's ability to cross over the line from comedy to drama, and cast him in the dramatic role of a priest whose parish is a small mining town in 192l and who falls in love with a young nun assigned there.

The movie is "The Runner Stumbles," based on a 1976 Broadway play. The nun is portrayed by Kathleen Quinlan, 23, the sick girl in "I never Promised You a Rose Garden."

Roslyn is a city of about 1,000 that has changed little since the coal mines closed years ago. Television came here only recently, cable bringing in the signals from Yakima. The permanent town storefronts were just fine for this movie.

This is Van Dyke's kind of country. Years ago, he picked up and moved his family from Los Angeles to Carefree, Ariz, a desert town not far from the somewhat but not much larger Cave Creek, 45 miles north of Phoenix.

There are four children. Living at home is daughter Carrie, a high school senior. The others are Christian, 28, a deputy district attorney in Salem, Ore.; Barry, 27, an actor, and Stacy, 23, a singer in Scottsdale.

Van Dyke was apprehensive about this movie. "I told Stanley I was putting myself totally in his hands." he said. What Kramer ordered was a complete makeover. Said Van Dyke, "He told me, 'I'm convinced you can do it but I don't want to see a vestige of Dick Van Dyke in this part, not a word, not a body movement.'

"I've had to change my whole personality. In some places, the slightest turn and I could fall into comedy and make people laugh.

Kramer, who produced "High Noon," "The Wild One" and "Home of the Brave" and directed "The Defiant Ones," "Judgment at Nuremberg" and "Guess Who's Coming to dinner," had considered filming "The Runner Stumbles" for a couple of years.

Like his other films, "Runner" delivers a statement, this one about love and commitment and the conflict between himan emotions and spiritual ones.

Van Dyke found his character "a man with lots of repressed anger who entered the clergy for the wrong reasons. He didn't care for the secular world and the priesthood was an asylum.

"The question of commitment interests me. These days the word doesn't mean much. This man goes through real abony about his commitment. What he faces is a young mun's reasoning that human love is a much a gift from God as anything else."

Van Dyke has carved, as one observer put it, "a G-rated image" from his television shows and such movies as "Bye, Bye Birdie," "Mary Poppins" and "Chitty Chitty Bang Bang." He has occasionally, however, hinted at more. There was an introspective and bitteresweet performance in "The Comic," a film directed in 1969 by his firend Carl Reiner. And there was a memorble TV movie in 1974 called "The Morning After," the story of an alcoholic to which Van Dyke brought some personal experience.

"I want to say that this movie is not onlu about religion but it's a murder mystery as well (the nun is killed) and a love story. It is about two human beings who do their best to be Christ-like but who have all the frailties human beings do."

Van Dyke looks toward more serious roles. "People don't like it when you change," he said. "For me, though, being dependable is not the most fun.

There are new Broadway offers, too. His run last year at the Huntington Hartford in "Same Time, Next Year" with Carol Burnett "was much too short for me. It was 18 years since I'd been on stage and I realized that's why I went into the business.

Van Dyke may also play Fearless Fosdick in an hour comedy for NBC that could turn into a series. "I'd be an American Inspector Clouseau," he said.