Nearly 100 U.N. Ambassadors went to Pennsylvania yesterday to see and be seen during a whirlwind public relations spectacle designed to display a slice of typical American life.

In 15 frenetic hours, the diplomats visited a university, toured a steel mill, rode on riverboats, watched a baseball game and were greeted everywhere by marching bands and majorettes before they were scheduled to see a Fourth of July-style fireworks show.

If the VIP pampering by personal military escorts and the hoopla that followed the dignitaries constantly during the carefully orchestrated tour didn't seem like a slice of ordinary AMerican life, the diplomats didn't let on.

In all, 400 foreign officials, wives an newspeople-four planeloads-were airlifted from New York to this industrial city in a one-day, $200,000 junket whose purpose-both the hosts and the guests frankly acknowledged-was to proselytize one another. The trip was paid for entirely from donations, most of them made by corporations.

For Pennsylvania and the city of Pittsburgh, it was a chance to sell the state's industrial potential and attract foreign investment.

For the diplomats and the sponsoring United nations Assn. of the U.S. it was an opportunity to promote the world organization, while at the same time giving the ambassadors a chance to get out of Manhattan.

"It's a wonderful opportuniy for everyone and quite spectacular," said U.N. Secretary General Kurt Waldheim as he and the other guests sweltered in 2,900-degree heat from a furnace at U.S. Steel's Homestead plant.

Earlier, Wadheim was presented the annual George C. Marshall Peace Award.

In a speech, Waldheim urged the creation of an International energy institute, not necessarily a part of the nations in exploring for new energy sources.

The generosity of the dozen or so private groups and companies who sponsored the U.N. visit seemed limitless. The contingent arrived aboard four DC-9s donated by Allegheny Airlines and were met by 150 rented cars provided by the Hertz Corp., each with a National Guard driver and an escort driver conscripted for the occasion by Gov. Milton J. Shapp.

They were taken to the University of Pittsburgh, where they were each given a silver commemorative medal specially minted, the program carefully noted, by the Franklin Mint of Philadelphia.

After viewing a slide show extolling the virtues of Pennsylvania, they lunched at the Carnegie Institute Museum of Art, where at each table was seated a representative from Pennsylvania industry "available to answer questions about the state," a Chamber of Commerce spokesman explained with a straight face.

The diplomats, donning shiny white hardhats imprinted with the U.S. Steel's logo, then went by bus to the Homestead mill, where briefly watched the rolling of three-quarter-inch plates for a new Great Lakes tanker.

Again, public relations aides hovered around the U.N. officials ready to answer questions.

Later, the dignitaries rode down the Monongahela River on two replica paddlewheelers, courtesy of the Gateway Clipper Fleet, the program carefully noted.

When asked if foreign trade ministers wouldn't have been more likely targets for such a promotional trip, U.N. Assn. publicist Michael Moynihan said, "These folks (the Pennsylvania promoters) will take what they can get. Maybe the ambassadors will put in the one good word that sways somebody."

Moynihan is the brother of former U.N. ambassador Daniel P. Moynihan, now New York's junior senator.

One Chamber of Commerce official said the Pennsylvania stepped up its promotional efforts after Volkswagen began builing a plant in New Stanton, which will begin producing cars next year. The plant will create 5,000 new jobs directrly and 35,00 jobs including support industries.

Conspicuously missing from most of the day's activities was U.S. ambassador Andrew Young who, because of other commitments, didn't join the group until the third inning of the Pirates-San Diego Padres baseball game, which the diplomats saw.

In an impromptu news conference at the ballpark, Young defended his controversial remarks about racial discrimation, saying he felt they had raised the public's consciousness about human relations. "Whether it's raised the understanding is another question," he said.

"I don't think the criticism (of the remarks) has been that bad as you look around the country. I have no complaints," Young said.