WASHINGTON — Two leading senators have asked the Obama administration to warn South Korea against allowing Huawei, the Chinese telecommunications firm, to build large parts of a next-generation network for the capital city of Seoul, arguing that it could give the Chinese government a way to enter the networks of a major American ally.

The issue appears almost certain to come up when Vice President Joseph R. Biden Jr. arrives in Seoul later this week, the last stop on his Asian trip.

At a moment when the United States is already protesting China’s establishment of an “air defense zone” over disputed territory in the East China Sea, the Huawei issue is bound to be another irritant in an increasingly contentious discussion with the government of the Chinese president, Xi Jinping.

The White House would not say whether Mr. Biden was planning to bring the issue up with the leadership in Seoul.