Democratic National Chairman John C. White yesterday escalated his attempts to head off opposition to President Carter within his own party with a series of harsh lectures to party leaders.

Calling Carter's record during his first two years in office better than that of any president in modern history, including Franklin D. Roosevelt, White urged party leaders to close ranks around the president.

"Jimmy Carter has something going for him that few presidents can claim," White said. "He has America at peace and he has America at work."

White made his comments in a series of speeches as the Democratic National Committee began the first of two days of meetings here. It was the second day in a row that he has issued strident calls for party unity in an apparent attempt to cut off a growing number of efforts to draft Sen. Edward M. Kennedy (D-Mass) for the 1980 Democratic nomination.

When a group of congressmen announced one such effort Tuesday, White accused them of attempting to "hand over the presidency on a silver platter to John Connally or Ronald Reagan."

White didn't mention the Kennedy efforts yesterday. But he used the same indignant manner and many of the same words.

During a caucus of midwestern Democrats, for example, he said: "The Republicans think they're going to take the Senate and take the presidency away from us. And they're going to take it away in the Midwest."

Carter, who has suffered a series of legislative defeats this week, is scheduled to speak before the entire committee today.

In other business, the party's executive committee yesterday voted to begin its next nominating convention on Aug. 11, 1980, one month later than the Republicans, amid increasing signs that it will be held in New York City, the site of the 1976 meeting.

Three other cities, Philadelphia and Detroit, where the Republicans plan to hold their convention, and Dallas, are still in the running, and have yet to be visited by the site selection committee.

Each of the cities presents major problems, however, and only New York has the 17,500 to 20,000 rooms necessary for the convention readily available. If, Detroit were picked, for example, hundreds of delegates would have to sleep in dormitories at the University of Michigan in Ann Arbor.

If it were held in Philadelphia, hundreds of delegates would be housed in Atlantic City, N.J.