President Reagan will step away from inaugural festivities on Sunday long enough to toss the coin that will determine who kicks off Super Bowl XIX in Palo Alto, Calif. Reagan's toss will be beamed by satellite to the site of the game and aired live on ABC-TV, it was announced yesterday.

Visiting team captain Dwight Stephenson of the Dolphins will call heads or tails (heads on the commemorative coin is a picture of Vince Lombardi), former NFL running back Hugh McElhenny will relay the choice to Reagan by telephone, and the president will officially toss the coin. Revealing the plans at a White House press briefing, spokesman Larry Speakes said the coin toss would be "the only connection between the Super Bowl telecast and the inaugural festivities taking place in Washington."

But a spokesman for ABC News and Sports said Reagan will also be on the phone at the end of the game to make the traditional presidential congratulatory call to the winning team's coach. A request for a separate, exclusive interview with Reagan, to be conducted by ABC's David Brinkley and Peter Jennings, was turned down, an ABC News spokesman said yesterday. It might have aired at halftime during the game if granted, though the logistics of that had not been worked out.

When ABC reporter Sam Donaldson asked about the status of the interview at the briefing, Speakes reportedly became angry and growled at Donaldson, "I'd keep my mouth shut if I were you. Your network is concerned. I'm really ticked." Speakes said it was his "standing policy" not to reveal to the competition when an exclusive presidential interview is granted. But Donaldson said he wasn't the competition, he was ABC News.

The exact location for the president's coin toss has not been determined.