VENICE, JUNE 12 (FRIDAY) -- President Reagan, in a speech for delivery today in West Berlin, challenges Soviet leader Mikhail Gorbachev to tear down the Berlin Wall "if you seek peace."

The speech, to be delivered at 8 a.m. EDT at the Brandenburg Gate in full view of the barrier between East and West, proclaims, "The wall cannot withstand freedom."

"General Secretary Gorbachev, if you seek peace, if you seek prosperity for the Soviet Union and Eastern Europe, if you seek liberalization, come here, to this gate," Reagan says in the speech, distributed to reporters yesterday.

"Mr. Gorbachev, open this gate," Reagan taunts. "Mr. Gorbachev, tear down this wall."

About 20,000 people marched through West Berlin last night to protest Reagan's visit, denouncing U.S. policies in the Middle East and Persian Gulf and demanding nuclear disarmament.

Afterward, small bands roamed the steets, smashing windows, torching police barricades and ripping up cobblestones to hurl at police. No injuries were reported.

The president, accompanied by his wife, Nancy, was to travel early today from Venice -- where Reagan attended the three-day economic summit -- to West Berlin to celebrate the city's 750th anniversary.

The visit was to be the president's second to the divided city, where in 1982 he delivered a speech and jokingly put his foot over the line into East Berlin at Checkpoint Charlie.

In the speech scheduled for today, Reagan follows the footsteps of his predecessors -- starting with President Kennedy, who proclaimed "Ich bin ein Berliner" (I am a Berliner) -- in adopting German language to express solidarity with the people of the city and denounce the wall that divides it.

"You see," the speech says, "like so many presidents before me, I come here today because wherever I go, whatever I do, 'Ich hab noch einen koffer in Berlin' (I still have a suitcase in Berlin)."

Describing the fortitude of the city's inhabitants, Reagan said they have "Berliner Herz, Berliner Humor und Berliner Schnauze" -- Berliner heart, humor and spirit.

In his opening remarks, Reagan extended the "warmest greetings" of the American people to the people of Eastern Europe, some of whose leaders turned a cold shoulder on Gorbachev when he visited Warsaw Pact nations recently to pursue his campaign for glasnost, or openness.

"Although I cannot be with you," Reagan said, "I address my remarks to you just as surely as to those standing here before me. For I join you as I join your fellow countrymen in the West in this firm, this unalterable belief: 'Es gibt nur ein Berlin!' (There is only one Berlin)."

The president questioned whether Gorbachev's glasnost campaign signals "profound changes" in the Soviet Union or token gestures "intended to raise false hopes in the West."

"There is one sign the Soviets can make that would be unmistakable, that would advance dramatically the cause of freedom and peace," he said. That, he said, would be to tear down the Berlin Wall.

In anticipation of anti-American demonstrations, the president invited all who protested against the deployment of Pershing medium-range missiles in Europe, and "those who protest today," to mark the fact that the Soviets came back to the nuclear arms bargaining table "because we remained strong."

Taking note of German concerns that removal of intermediate-range missiles from Europe could leave them vulnerable to superior Soviet conventional forces, Reagan said, "While we pursue these arms reductions, I pledge to you that we will maintain the capacity to deter Soviet aggression at any level at which it might occur."