The survey, conducted on Feb. 24-28 by independent pollster Social Weather Stations (SWS), showed 36 percent of 2,100 respondents preferred Aquino, the son of the country's democracy icon, Corazon "Cory" Aquino.
Support for his nearest challenger, billionaire lawmaker Manuel "Manny" Villar, fell by one point but Villar was within sight of Aquino at 34 percent - inside the poll's margin of error of +/- 2 percent.
Backing for Aquino, a reluctant candidate who has vowed to continue his parents' fight for clean government, had stood at 42 percent in the previous SWS poll released on Jan. 10.
"If you look at our series, steadily the lead is getting narrower and narrower," said SWS head Mahar Mangahas.
Mangahas did not give a possible reason for the consistent fall in support for Aquino but said the latest poll showed there was no clear leader.
Aquino's ratings peaked at 60 percent in September 2009, shortly after he announced his candidacy for the May 10 presidential polls, but dropped to 46 percent by December.
Former president Joseph "Erap" Estrada and administration candidate Gilberto "Gibo" Teodoro both gained two points 15 and six percent respectively.
"Surveys cannot really predict the outcome of elections," said political science professor Ronald Holmes, head of rival pollster Pulse Asia Inc.
He said the political machinery of major parties would also come into play when campaigning for local positions begin later this month.
Holmes said former congressman Jose de Venecia had trailed in all opinion polls during the 1998 presidential polls but eventually came a strong second because of the efforts of his party machine. Nearly 50 million Filipinos will select a president, a vice president, nearly 300 lawmakers in the two houses of Congress and more than 17,500 local positions.
