Has President's strength in polls reached its peak?

The public opinion teeter-totter, which has pitched Sen. Edward M. Kennedy down and President Carter up in the Democratic standings since last summer, may already have begun to tilt the other way, public opinion analysts warn.

The President's "decisive" 58-to-38 percent edge over Mr. Kennedy among Democratic voters, as reflected in the latest ABC News-Louis Harris survey, may prove as ephemeral as the Senator's 60-to-35 margin over Mr. Carter last September, they say.

There are two reasons for taking the poll data with caution:

First, the just-published samplings of opinion were taken in mid-December. Since then, as even White House sources reportedly suggest, support for the President over Iran may have peaked. The lingering standoff over the hostages may have begun to breed public impatience and frustration, added to by the Soviet incursion into Afghanistan. Mr. Carter's Republican rivals already have begun to link his "patience" with "weakness." This must benefit his Democratic rivals, Senator Kennedy and California Gov. Edmund G. Brown Jr., political analysts assume, whether or not those two Democrats are emboldened to criticize the President's foreign affairs leadership.

Second, there is a far higher level of indecision among voters than the poll numbers suggest, public opinion analysts say.

"Undecideds are terribly important in trial heat comparisons," says Everett Ladd Jr., director of the Social Science Data Center at the University of Connecticut. "There are more undecideds than the numbers show. There are genuine undecideds, and others who say they are decided but really aren't.

"As of last July 1, if 85 percent chose between Kennedy or Carter, perhaps 60 percent hadn't really made any choice at all in who they actually favor for the presidency," Mr. Ladd says. "Now, of 85 percent choosing between candidates, maybe 50 percent -- nobody really knows -- are actually undecided. This number will continue to shrink as people move from the vague, hypothetical phase of the election process toward the realities of the primaries and the convention."

Adding to the indefiniteness of current poll samplings, even the remaining 15 percent who chose "no-opinion, don't know, or undecided" options may be no more undecided than a similar group who make a choice, Mr. Ladd says. Many people who have made a choice often prefer not to say so.

Meanwhile, the undecideds will likely play a crucial role in the first actual test of the 1980 campaign, the Iowa caucuses Jan. 21. Iowa poll results, also taken mid-December, showed President Carter and Senator Kennedy in a dead heat, with 10 percent undecided. However, the indecision level is far deeper in Iowa than those figures show -- both in attitudes and in the way Iowans perform as delegates, both sides say.

"We've found an extraordinary number of undecideds in Iowa," says Kennedy spokesman Thomas Southwick, commenting on the campaign's polling and telephone findings. "Many Iowans were waiting for the debates to help them decide. What they'll do now, I don't know."

"There's a strong uncommitted tradition here in Iowa," says John Law, executive director of the Iowa Democratic Party. "People forget that in 1976, in the Iowa precinct caucuses, 'uncommitted' was the actual winner."

In the January 1976 precinct caucuses, 38.5 percent of the caucus delegates declared themselves uncommitted, with only 29.1 percent for Mr. Carter. At the next caucus stage that year, the county caucuses in March, the number of uncommitted delegates swelled to 40.9 percent, with Mr. Carter getting 34.2 percent and US Rep. Morris K. Udall of Arizona, 12.9 percent. By the April congressional district caucuses, the uncommitted controlled 32.7 percent of the votes, Mr. Carter 39.3 percent, and Representative Udall 23 percent.And at the state convention final in June, the uncommitted still held 27.9 percent, Mr. Carter 42.3 percent, and Mr. Udall 28.4 percent.