(Recasts, adds comments by S&P analyst, background)

By Walter Brandimarte

NEW YORK, June 11 (Reuters) - Standard & Poor's said on Thursday it will not have the information to decide on a possible downgrade of Mexico's credit ratings until the last quarter of this year, after Congress approves the budget for 2010.

"It is later on in the year that you will have more information" to decide on the ratings, S&P analyst Lisa Schineller told Reuters in an interview.

"First you have elections in July, then the budget goes in September, and discussions over different pieces (of the budget take place) in October and November," she noted.

Mexico's currency and bonds were pressured this week by speculation of an imminent downgrade of the country's credit ratings.

S&P in May revised its outlook on Mexico's BBB-plus credit ratings to negative from stable, saying it might downgrade the ratings if the government failed to address pressing fiscal issues later this year.

Investors are particularly concerned that President Felipe Calderon will not get enough political support to pass reforms that would broaden Mexico's tax base and reduce its reliance on oil revenues.

In an interview with Reuters on Tuesday, the head of Mexico's ruling National Action Party, or PAN, said the party will not support tax reforms "under any circumstances." For details, see [ID:nN09348858].