Three polls released this weekend show Democrats leading in the contest for House seats, while a national poll shows President Reagan maintaining a wide lead over Democratic nominee Walter F. Mondale.

A Gallup Poll finds the race for House seats virtually deadlocked, with Democratic candidates likely to receive about 51 percent of the vote, compared with 49 percent for Republican candidates. That margin is substantially smaller than the 55-to-45 percent lead at the same point in the 1980 campaign.

The latest Harris Survey finds that Democrats have a 52-to-41 percent lead over Republicans for control of the House, up from 50 to 42 percent earlier this month. In the race for Senate seats, the Democrats are holding onto their 51-to-43 percent lead.

According to a Newsweek poll, 49 percent of persons surveyed said they intend to vote for a Democratic congressional candidate, and 44 percent said they will vote for a Republican. The poll also showed Reagan leading Mondale, 57 to 40 percent.

Meanwhile, a USA Today poll to be published today shows the president maintaining a 23-point lead over Mondale, 59 to 36 percent. A poll published yesterday in the Lincoln (Neb.) Journal-Star shows 70 percent of Nebraskans favoring Reagan and 24 percent favoring Mondale.