U.S. stock index futures were flat on Tuesday ahead of critical debt limit talks, and retail sales data that will offer more insight on the economy's health, while Capital One shares jumped after Berkshire Hathaway revealed its stake in the company.

The main indexes started the week with modest gains as trading was range-bound amid a wrangling in Washington between the White House and Republicans on whether the $31.4 trillion debt ceiling stands to be raised to avoid a default as a little more than a two-week deadline loomed.

Focus will also be on economic data, with retail sales expected to increase 0.8% in April, after falling 0.6% in the month before.

Data recently has pointed to a slowing U.S. economy, which is starting to feel the effects of the Federal Reserve's restrictive monetary policy, and also heightened expectations for when the central bank will pause its hiking cycle.

At 5:38 a.m. ET, Dow e-minis were down 27 points, or 0.08%, S&P 500 e-minis were down 2.75 points, or 0.07%, and Nasdaq 100 e-minis were up 3.5 points, or 0.03%.

Shares of Capital One Financial Corp jumped 6.8% in premarket trading after Berkshire Hathaway Inc on Monday disclosed it has begun investing in the consumer lender.

Berkshire also upped its stake in HP Inc, sending its shares up 1.5%, while shedding stake in regional bank US Bancorp, which slipped 1.4%.

(Reporting by Shreyashi Sanyal in Bengaluru; Editing by Maju Samuel)