A new Louis Harris poll of likely voters nationwide gives Republican presidential nominee Ronald Reagan a huge lead over President Carter, his probable Democratic opponent.

The survey, broadcast last night on ""World News Tonight" (ABC-WJLA), shows Reagan winning the support of 61 percent of those interviewed, with 33 percent for Carter. This is one of the largest start-of-the-campaign leads in the history of the Harris Survey -- but not as great as Carter's 62-to-27 lead over then president Gerald R. Ford at the same point in the 1976 campaign.

The survey, taken last weekend just after the Republican National Convention, shows that Reagan got a big boost from the four nights of prime-time coverage of the events in Detroit.

A Harris Survey of likely voters taken three weeks before the convention had Reagan leading Carter 51 to 44 percent.

The latest poll asked respondents to choose between Reagan and Carter, without mention of independent hopeful John B. Anderson or other presidential candidates.

The new Harris figures are roughly in accord with those in an Associated Press-NBC survey released earlier this week. That poll also taken just after the GOP convention, gave Reagan a 55-to-24 percent lead over Carter, with 15 percent preferring Anderson. The AP-NBC poll surveyed only voters who said they have made up their minds about whom they will vote for -- a somewhat different sample from the "likely voter" category used by Harris.

Most nominees in recent history have surged in popularity immediately following the conventions that selected them. The historical pattern suggests that, other things being equal, the Democratic nominees should close the gap with Reagan after the Democratic convention in New York Aug. 11-14.

In 1976, for example, Carter led Ford 53 to 40 percent in the Harris poll taken just before the Democratic convention. After his nomination Carter jumped to the 62-to-27 lead. A month later, after Ford's nomination, Carter's lead was narrowed to 49 to 38. And by the last Harris poll of that election year the two were almost even.

With that history in mind, pollsters have suggested that between-conventions polls be read with some skepticism.

"The between-conventions measurement is almost always moved out of focus because of the imbalance of media and publicity [focused] on one party during the convention, said Burns W. Roper of the New York based Roper Organization.

Still, the latest polls reflect a general trend seen in almost all presidential preference surveys since spring -- Reagan catching and then passing Carter.

A Harris poll in February gave Carter a 64-to-32 percent lead over Reagan -- just about the reverse of the latest survey. Similarly, Gallup polls have seen Reagan move from a hefty deficit last winter to a tie by late spring; in the latest Gallup poll taken just before the Republican convention, respondents favored a Reagan-George Bush ticket over a Carter-Walter Mondale ticket by 9 percentage points.