Writing a book about television evangelists is as risky as writing about politics. Yesterday's conclusions have a way of becoming quickly outdated.

Jeffrey Hadden, a University of Virginia sociologist who has established himself as one of the country's leading students of electronic religions, took both risks in "Televangelism: Power and Politics in God's Country," written with Anson Shupe, of Indiana University.In their book, Hadden and Shupe make the case that Pat Robertson could win the Republican Party nomination for president.

But Robertson's candidacy was dead after he finished third in South Carolina - a state he had once boasted of winning - and buried after he came up empty in the Super Tuesday primaries in the South.

Robertson failed to mount a serious challenge to George Bush, even though he beat the vice president in the Iowa caucuses, and Hadden believes it is an open question whether the Christian right is capable of electing a candidate.

Hadden and Shupe argue that a candidate from the Christian right stands to benefit from these factors:

-President Reagan has legitimized religious conservatism.

-The religious right overwhelmingly dominates religious broadcasting.

-Ministries such as Robertson's "700 Club" have developed impressive fund-raising skills.

-There is evidence of a conservative shift in the electorate.

The reality, though, was that Pat Robertson couldn't win this year.

Robertson's failure, Hadden said in a recent interview, was a combination of mistakes and a miscalculation of his base of support.

"He got so tangled up in his own words, and his own gaffes, that once he had attention there was never a moment to say, `This is why I have a better vision for America.'

"He also erred very badly," Hadden said, "in not addressing the religion issue head-on very early."

Robertson also overestimated the size of his base, Hadden said.

"He had measured the size of the evangelical Christian vote, and mistook it for his core constituency, which is charismatic," he said.