The race to be Provost of Trinity College is one of the closest for many decades, with three candidates regarded as potential winners of today's election.

Most observers still believe Prof John Hegarty, the university's dean of research, to be the front-runner.

But the chance of Trinity electing its first woman provost, Prof Frances Ruane, is a strong possibility.

The fortunes of the leading candidates have changed several times in the last month. Initially Prof Hegarty, a physicist, was certain to win, but then Prof Ruane, an economist, fought back with an energetic campaign highlighting her record as college bursar. Sources said her campaign was also boosted by favourable coverage in two Sunday newspapers.

In the last fortnight both candidates have been intensively lobbying the 520 staff members eligible to vote. But their efforts have been matched by Prof David McConnell, a scientist, who pulled off a coup by receiving the endorsement of Trinity's students' union, which has 11 votes.

Prof McConnell is regarded as a dark horse in the race, although if he is eliminated, his voters are expected to transfer their allegiance to Prof Hegarty, possibly because the two share a scientific background.

The big division in voting is between the arts faculty (mainly supporting Prof Ruane) and the science and medicine faculties which are mainly supporting Prof Hegarty or Prof McConnell, who has been involved in Tallaght Hospital.

The other candidates, Dr Micheal Mac an Airchinnigh, a computer scientist, and Prof Patrick O'Meara, a Russian lecturer, are trailing the three front-runners. However, Dr Mac an Airchinnigh, whose campaign has won the admiration of many, is expected to poll well. His supporters are expected to transfer mainly to Prof Hegarty, while Prof O'Meara's supporters are likely to roll in behind Prof Ruane.

The former president, Mrs Mary Robinson, who is Chancellor of Dublin University, is expected to arrive before the election. Supporters of Prof Ruane were hoping this week their candidate, by winning this post, could emulate Mrs Robinson, who became the first woman president of Ireland.

The election to the £100,000-a-year post entails eliminating one candidate each round until two remain and they have a straight run-off.

A fresh vote takes place each round, and a result is expected shortly before lunchtime.