A few minutes before 10:30 a.m. each weekday, the man his staff called the "Johnny Carson" of television evangelism receives a touch-up in his makeup room, smoothes out his three-piece pastel suit and strolls onstage in his Portsmouth, Va., studio to upbeat band music and excited applause from his audience.

As host of "The 700 Club", an entertaining religious talk show seen here weekdays at 10 a.m. on Channel 20, the Rev. M.G. "Pat" Robertson has changed the style of TV evangelism. His soft-sell program, which offers penetrating interviews, fervent prayers for 1.25 million callers annually and upbeat "Top 40" in gospel tunes drives home the same conservative Christianity as its competitors, but without the breast-beating that dominates most religion on the air.

That feverish evangelism has also characterized the ministry of another giant in the business, Rex Humbard, who left his father's itinerant ministry 25 years ago for a career he presently recognized in television.

What the world needs, says Humbard, whose programs are on more stations than any other evangelist (Channel 20, 8:30 Saturday mornings), is an "old-fashioned holy ghost, God-sent, soul-savin', sin-killin' revival when people get right with God."

TV evangelists currently buy $500 million annually in air time to televise the 56 regular religious programs that reach an estimated 13,259,000 households each week. Oral Roberts commands first place with 23 million households weekly, and Humbard's audience ranks second, with 1.68 million, according to November, 1976, Nielsen ratings.

Next is a low-key Bible study show, "Day of Discovery," and Robert Schuller, who promotes an optimistic "possibility thinking" from his drive-in church near Disneyland, is fourth.

Robertson, who stands 19th with 173,000 households weekly, represents the new breed of enterainment-oriented evangelist whose imagination has influenced the entire industry. Humbard is more of a traditionalist.

The son of former Virginia Sen Willis Robertson, a graduate of Yale Law School and a Pentecostal Christian who believes in divine miracles and is forthright about the emotional appeal of his faith, Robertson is as composed as any veteran television host. He cracks jokes and he adeptly draws out his guests.

"His approach is positive and supportive rather than negative and judgmental," observed Dr Ben Armstrong, executive secretary of National Religious Broadcasters. "While Billy Graham 'proclaims the World,' Pat lets people tell their own stories. He excites his audiences with his questions."

Concerned with freeing conservative Christianity from what he calls its "fortress mentality," Robertson invites his guests from a wide swath of "born-again" personages - celebrities like singer B J Thomas, political figures like ex-Black Panther Eldridge Cleaver, sports notables like Dallas Cowboys' coach Tom Landry and unknown homemakers and blue-collar laborers. His intention is to let them convert viewers by their personal stories. His staff estimates the 30,000 viewers "accept Christ" each year by watching "The 700 Club," many indirectly through telephone counseling offered off-camera.

It's a homey show and Robertson is "Pat" to everybody. "People treat him like a personal friend," said Scott Hessek, spokesman for Robertson's diversified Christian Broadcasting Network in Virginia Beach, Va.

"I've seen 70-year-old ladies run up to him in airports and kiss him," he said, "Can you imagine calling Johnny Carson 'Mr Carson?'"

Robertson has also discarded the traditional evangelical taboo against politics. In 1974 he rapped former President Nixon on the air, saying the chief executive had perpetuated a "cruel hoax" on the American people. Last year, he had as his guest a man who with Robertson's support became the front-running winner in a city council election.

The boyish-looking 47-year-old Robertson walks modestly among the high and the mighty, according to associates, and admits he has considered public office himself. For the present, however, "Jesus has not told me" to pursue a political career, he said in an interview.

Arkansas-born Humbard leaves politics and controversy to others. He prefers the basics. "I feel there is a breakdown in the home, in family life," he said in a recent interview. "I use psychology and common sense and talk about 'don't lie, don't steal' and so forth. This is universal."

Consequently Humbard's show sounds pretty much the same each week. With 13 members of his family in tow in long frilly gowns and plain dark suits, from wife, Maude Aimee, to his grandchildren. Humbard appears on a stage which rises and falls by hydraulic lifts in the $3.5 million "Cathedral of Tommorrow." The 5,000 seat auditorium in Akron, Ohio, is drapped in plush velour and red carpeting.

Often his show is taped during one of his worldwide jaunts. "I probably travel 300,000 miles in a 12 month's period" said Humbard. "I'm always tired. I was born tired. But you have to love it." Humbard's troupe went to Australia this month where they hauled $1 million of their $8 million in production equipment for "quality control" of the programs.

Like Robertson, Humbard said his organization receives about $18 million a year, mainly in donations of $5 and $10 from viewers. That money is quickly parlayed into spreading the TV ministry. Humbard's show is seen on 223 stations in the U.S. and 317 overseas on every continent but Antarctica. He's dubbed in seven languages at his Akron studios. "We still have half the world's population to reach," he said with a sweeping gesture.

"Let's face it," Humbard added, "if we don't go into the public media, we won't got them into the church."

Robertson has the same idea. Last month, CBN inaugurated a $500,000 satellite which will facilitate simultaneous broadcasts of "The 700 Club."

By the fall of 1978, CBN's broadcasting school, which will teach the "psychology of persuasion," is expected to open on a 142-acre, $25-million CBN development at Virginia Beach. The complex eventually will include a college, a school of theology, studios, dormitories and an auditorium.

"There is no question," said the man who started his venture in 1959 with $70 in his pocket, "that there is nothing as effective in the whole world as television." CAPTION: Picture 1, "TV evangelists currently buy $500 million annually in air time to televise the 56 regular religious programs that reach an estimated 13,259,000 households each week."; Picture 2, Pat Robertson with President Carter in Plains, Ga.