WASHINGTON — President Obama has persuaded some of the nation’s largest companies, including Walmart, Apple, General Motors and Ford, to revise their hiring practices to avoid discriminating against applicants who have been out of work for a long time.

Mr. Obama hosted a group of corporate chief executives at the White House on Friday to highlight those efforts and the use of presidential persuasion to help the jobless find work.

White House officials said that about 300 businesses, including 21 of the nation’s 50 largest companies and 47 of the top 200, had agreed to new hiring policies that ensure applicants who have not worked in a long time are not unfairly screened out.

“Folks who’ve been unemployed the longest often have the toughest time getting back to work,” Mr. Obama said at the event. “It’s a cruel catch-22 — the longer you’re unemployed, the more unemployable you may seem. Now this is an illusion, but it’s one that, unfortunately, we know statistically is happening out there.”