"That is possible yes, the wider the menu of options for Malacañang, insofar as the administration senators are concerned, the better because they will be able to find the administration candidate who has the widest support among the independent (senators) and among the opposition," Santiago told reporters seeking comment.
Roxas has refused to answer reporters questions on the unconfirmed plan by the Palace to support him as a possible replacement for Drilon, who has been at odds with the Palace since he called for Mrs. Arroyos resignation in early July over allegations that she cheated in last years presidential election.
Sen. Lito Lapid was quoted in radio reports as saying that Mrs. Arroyos political adviser on legislative affairs, Gabriel Claudio, had mentioned Roxas a neophyte senator who topped the elections last year as Drilons possible replacement.
Drilon, along with some members of the Liberal Party that included Senate Majority Leader Francis Pangilinan, joined the opposition-led call for Mrs. Arroyos resignation following her admission that she phoned an election official during the presidential vote count.
Roxas, also a Liberal, however kept his distance from his partymates stance.
The President denied rigging the outcome and rejected calls for her resignation.
Drilon has since said he is not keen on keeping his post, and would give it up once any contender musters at least 13 Senate votes to oust him.
Sen. Sergio Osmeña III earlier described Drilon as being "a Senate president in sufferance," meaning that he was merely being tolerated by his colleagues.
Santiago, an Arroyo ally, was said to be aspiring for the Senate presidency, and has noted that only she would have support from the administration and the opposition, through her earlier support of ousted President Joseph Estrada.
However, Sen. Manuel Villar, chairman of the Senates committee on public order and illegal drugs, as well as the committee on finance, has a term-sharing agreement with Drilon, which is set to turn over to him in January.
Villar, who was seeking the Senate presidency after the last election, gave way to Drilon after reaching a term-sharing arrangement to keep relations smooth between them.
But if Malacañang endorses Roxas, this would minimize Villars chances of taking over the Senate presidency.
Although Villar was recently lauded by Mrs. Arroyo in one of her speeches for pushing the passage of the anti-terror bill, the President is unlikely to forget that Villars wife, Las Pinas Rep. Cynthia Villar, backed the opposition-initiated impeachment complaint against the President.