The last poll before tonight's Republican presidential caucuses in Iowa found Bob Dole with nearly 30 percent support, ahead of a second tier with Pat Buchanan gaining among Christian Coalition backers and Steve Forbes suffering the wrong kind of momentum.

Former Tennessee Gov. Lamar Alexander also was in the hunt for second in the survey conducted Friday and Saturday by Mason-Dixon Political-Media Research.

Texas Sen. Phil Gramm, backing off his top-three-or-out vow, was tied with Indiana Sen. Dick Lugar and commentator Alan Keyes for fifth.

Polls conducted before past Iowa caucuses generally have succeeded in identifying winners but not at detecting likely runners-up _ who, like Gary Hart in 1984, can become prominent players in presidential nomination fights.

Targeting a small pool of likely caucus-goers _ turnout typically is 20 percent of a party's registered voters _ Iowa surveys can underestimate the impact of strong political organizations and highly motivated voting blocs.

This year, Dole, Gramm, Alexander and Buchanan have stressed their get-out-the-vote organizations, while publishing heir Forbes has spent at least $4 million of his personal fortune saturating the airwaves with attack ads.

Forbes had edged ahead of Dole, the Senate majority leader making his third presidential bid, in some surveys in recent weeks in Iowa and New Hampshire, the next campaign battleground. But now Dole has moved back ahead as Forbes' support diminishes and softens.

The Mason-Dixon poll and an Iowa Poll conducted last week by The Des Moines Register both found Dole with support from 28 percent of voters who called themselves likely caucus-goers.

Both polls had Dole clearly but not overwhelmingly in the lead, with the race for second and third a muddle. But Mason-Dixon found Buchanan with momentum, especially among Christian conservatives, who are expected to be a major force in the caucuses.

Among the 30 percent of likely caucus-goers who support the Christian Coalition, commentator Buchanan was favored by 34 percent, Dole 26 percent, Gramm 11 percent, Alexander 9 percent, Forbes 5 percent, Keyes 3 percent and Lugar 2 percent. Ten percent were undecided.

That was a 10-point jump for Buchanan from a Mason-Dixon poll conducted Monday through Wednesday. It was no real change for Dole and a 7-point drop for Forbes, who charged the day the new poll began that the Christian Coalition _ which has criticized his abortion stance _ ``speaks only for its members.''

The poll was finished before such late developments as the coalition's distribution of 250,000 voter guides at Iowa churches Sunday and a Forbes spree of half-hour TV infomercials.

Those were aimed largely at undecided voters _ 13 percent of Mason-Dixon's poll of 447 registered Iowa voters who said they were likely to attend a caucus. The margin of error was plus or minus 4 percentage points. Sponsors were the Moline Dispatch and Cedar Rapids Gazette newspapers and TV stations WQAD, KCRG and KCCI.

Dole had support from 28 percent overall, up 4 points from the previous Mason-Dixon poll, to 16 percent for Buchanan, 15 percent for Forbes and 12 percent for Alexander.

Buchanan, possibly riding a bounce from his upset of Gramm last week in Louisiana's limited caucuses, gained 5 points. Forbes, facing increasing media scrutiny and counterattacks to his self-financed ad blitz, was down 7 points.

Forbes also finds 60 percent of his supporters telling Mason-Dixon interviewers they could be persuaded to vote for another candidate, compared with 38 percent of Dole supporters.

Forbes was viewed unfavorably by 46 percent in the Iowa Poll, up 20 percentage points from December.

Forbes slippage also was apparent in new polls in New Hampshire, which holds its presidential primary a week from Tuesday.

Dole led Forbes 31 percent to 23 percent _ a reversal from two weeks earlier _ in a University of New Hampshire survey released Sunday by the Boston Herald and WCVB-TV, while a KRC Communications Research poll for The Boston Globe and WBZ-TV found Forbes slipping into a dead heat with Dole.

Dole and Forbes also were tied in results published today from a Gallup tracking poll in New Hampshire for USA Today and CNN.