In 1984, Orwell has O'Brien tell Winston why the Party seeks power. He says that it seeks power simply for the sake of power.
O'Brien tells Winston that the Party is different from all the other people or groups who have tried to wield the same amount of power. He says that those others have always at least pretended that they wanted power for some other purpose. They would talk about wanting to help their people, things like that. By contrast, the Party is totally honest -- all they want is power for the sake of power.
Here is a quote that shows this. It is from Chapter 20.
The Party seeks power entirely for its own sake. We are not interested in the good of others ; we are interested solely in power. Not wealth or luxury or long life or happiness: only power, pure power.
The previous post is accurate. From a political point of view, the party's desire to seek power is to consolidate control over the lives of its citizens and of Oceania. I think that Winston's statement is transparently valid, one of the few that can be deemed as such. The idea of the power wishing to seek power for its own sake, to greater maximize control over the lives of its citizens and of the nation, in general, is what defines their style of government. This form of rule eliminates the private realm entirely as a check or limitation. There is a great deal of intrusion and interference in the lives of its citizens because power and control know no limitations and few boundaries. It is with this in mind that the party is a construct and being of power, to be able to exert control and force in any realm it deems appropriate. Thus, the limitations on sexual conduct and the restriction of personal thought. The party seeks power because it is fundamentally driven to eradicate any possible threat to its control, and any possible alternative narrative.