President Reagan was loudly heckled today at the University of Portland, turning what began as a neatly scripted campaign rally into a boisterous shouting match.

It was the first time this year that protesters made it through the screening procedures Reagan-Bush campaign officials have used to keep protesters away from Reagan rallies. Two hecklers were forcibly ejected from the hall where Reagan was speaking.

James Lake, Reagan's campaign press secretary, said the heckling was organized by an "anti-Reagan coalition" and reflected "a certain amount of desperation on the part of partisans of the opposition." He noted that some of the protesters carried Mondale-Ferraro placards but added, "I don't mean to imply this is anything coming down from above."

Several protesters said they had acted spontaneously. Elliot Mantell, 33, a Portland chiropractor, said he came to present "another opinion" to the television cameras.

At a rally in Seattle, Reagan said Walter F. Mondale does not represent the kind of Democrat that the late senator Henry M. (Scoop) Jackson (D-Wash.) did on foreign policy and defense issues.

"On nearly every occasion that . . . Jackson cast a vote for America's defense, you would not only find Walter Mondale voting against him -- but on 37 of 38 times, you found him voting with George McGovern," Reagan said. "So, if you liked George McGovern's defense policies, you'll love my opponent's."

Mondale "seems to have a grudge against the future," Reagan said.

Fewer than two dozen protesters were inside the University of Portland's Earl A. Chiles sports arena, with signs having such messages as "The Reagan administration lies about Central America" and "The finger on the button is senile."

The hall, filled with 4,200 flag-waving Reagan supporters, was shown the Reagan campaign's 18-minute convention film. Reagan entered the hall as the lights came on and a huge American flag was raised behind the podium.

Against the backdrop of Reagan's standard stump speech celebrating optimism and prosperity, hecklers shouted epithets. "Liar, liar, pants on fire!" was one; others accused Reagan of being a "murderer" in Central America. "We don't want your war in Central America!" they chanted.

Reagan, told of the hecklers' plans in advance, ignored them at first. His supporters waved angry fists at the protesters and tried to smother them with "Oreagan" placards. The hecklers persisted with shouts of "Two more weeks!" and the Reagan supporters replied, "Four More Years!"

Responding to a solo heckler, Reagan shot back, "I may just let Mondale raise his taxes." When the heckling persisted, Reagan joked, "You know, I know I'm no concert baritone, so I know those can't be an echo in my voice."

The audience cheered, but the band of hecklers was not deterred, even when one blowing a whistle was carried out by student ushers wearing red Reagan-Bush shirts.

When Reagan said the American people "don't want" Mondale's tax increase, the protesters chanted back, "We don't want your war, either."

After a second heckler was removed, Reagan motioned to one side of the crowd and then the other. "There's a perfect example of where we solid citizens are -- caught between the right and left."

As he struggled to be heard at the close of his speech, Reagan said, "I'm going to finish this time."

The president said nothing about today being the first anniversary of the Beirut bombing of Marine headquarters in Lebanon.