(For full election coverage click on [ID:nN24156842])

* Ex-president and main rival too close to call

* One exit poll gives Kirchner narrow lead in key province (Corrects date of vote in fourth paragraph)

By Kevin Gray

BUENOS AIRES, June 28 (Reuters) - Former Argentine President Nestor Kirchner was neck and neck with his main rival in a key race in Argentina's congressional election, television exit polls said on Sunday.

When voting stations closed at 6 p.m./2100 GMT, television channel Todo Noticias said its poll showed Kirchner had a slight lead, but the station did not provide percentages and said the race was very close, implying the lead was within the poll's margin of error.

Other channels said the race was too close to call. The first official results were due at 9 p.m./0000 GMT.

Kirchner ran for Congress in Buenos Aires province to bolster his wife, President Cristina Fernandez, who is expected to lose her majority in Congress in Sunday's nationwide ballot, even if he wins the most votes in the province.

Kirchner, a Peronist, was running against millionaire businessman Francisco de Narvaez, a dissident from the same political party.