NEW YORK, June 11 (Reuters) - Standard & Poor's said on Thursday it will not have the elements to decide on a possible downgrade of Mexico's credit ratings until the last quarter of the 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's 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 Mexico'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 them if the government fails to address pressing fiscal issues later this year. (Reporting by Walter Brandimarte; editing by Leslie Adler)