Robertson tries to dent Bush lead. GOP frontrunner George Bush is expected to outpoll Pat Robertson in Florida's straw ballot on Saturday. But Robertson's crew hopes to make a good enough showing to cut into Bush's win. This would add credibility to the evangelist's campaign.

This Saturday, George Bush is expected to score a sweeping victory in the presidential straw ballot at the Florida Republican state convention. That could be his problem. Challenger Pat Robertson can carry away the campaign momentum just by putting a dent in Mr. Bush's showing.

The last time Florida Republicans held a straw ballot, in 1979, Ronald Reagan won. But Bush finished second, launching a surge of campaign momentum he called ``big mo.''

This year, Bush is the frontrunner, and Mr. Robertson, the evangelist broadcaster, is jockeying for position as a top-rank contender.

All the other Republican aspirants have bowed out of this peculiar contest - and potent media event - in the face of the special strengths of Bush and Robertson. No delegates are at stake here, only the frothy status of perceived winner and loser.

In Florida Saturday, Robertson will not have to win to win. If he can merely lose by less than expected, he will succeed in establishing the seriousness of his candidacy.

In the maneuvering to manage expectations, both campaigns are busy poor-mouthing their prospects, working to set themselves low benchmarks for success this weekend. Bush campaign manager Lee Atwater has said in recent months that the vice-president will do well to win 55 percent. The campaign's Florida spokesman, Jay Morgan, says more humbly that the Bush goal is to outpoll Reagan's 38 percent in 1979.

The Bush camp seeks to create a picture of a competitive contest where political observers say that Bush supporters have controlled the rules of the game and been able to handpick many of the voters.

The Robertson camp wants to paint a picture of a race where Bush controlled the rules, and where even a 20 percent vote Saturday means success.

Now that Robertson's Florida coordinator, David Zachem, knows who the convention delegates are, he will only say: ``I think we did very well.''

The voters in this straw ballot are not exactly a scientific sample. Nearly one in five will be party leaders, elected officials, and major donors. Of the rest, each county picks 30 percent of its delegation by executive committee and 70 percent by lottery.

Bush thoroughly dominates the structure of the Florida Republican Party. The governor and many party leaders are committed Bush loyalists. County by county, Bush organizers are working for a Bush blowout Saturday.

But this is also the kind of contest that Pat Robertson has shown he can win by working outside established party networks. In Florida, through churches, conservative mailing lists, and traditional-values organizers, Robertson is credited with converting many conservative Democrats into registered Republican activists. He is also winning support from many of the GOP's conservatives that would otherwise be supporting Rep. Jack Kemp.

Still, among Florida's Republican voters, a poll taken in early October by the Atlanta Constitution showed that 77 percent would not even consider voting for Robertson - a far higher negative response than for any other candidate.

That can change. Not many voters have heard Robertson speak. Bob Roman was a Democrat until Robertson spoke at his Pentacostal church last May in North Miami. Now Mr. Roman is Robertson's organizer in Dade County. The best recruiting ground for Robertson has been Christian churches, says Roman, where people are familiar with him from the religious talk-show program he hosted for years, the 700 Club.

Florida's most populous county, Dade, is Bush country. The county GOP was headed until recently by Bush's son Jeb, now state commerce secretary. Still, Roman figures that Robertson people drew about 20 percent of the county's lottery-drawn delegates.

In Broward County, another large delegation, Robertson was much more competitive. His supporters even managed to control the caucus committee that handpicked 30 percent of the delegation - a share conceded to Bush in most counties. Bush's Broward organizer Jim Blosser says that of 216 Broward delegates, the 20 to 25 that are still undecided will determine which candidate is ahead.

In Pasco county on the Gulf coast, charges of heavy-handedness by Bush organizers have cost them some delegates. County chairman Merle Conine, who personally supports Sen. Bob Dole, says, ``The Bush people could have had 40 of 67 delegates except for the heavy-handedness of their leadership.''

Sen. Robert Dole, although his name will not be on the ballot, will be in Florida this weekend working the convention. He is scheduled to leave before the balloting, however. Says Jay Morgan: ``The Dole people are now trying to have the best of both worlds'' - to score some points without joining the game.