Speaking behind a cordon of hundreds of riot control policemen who sealed off parliament, Chancellor Helmut Kohl declared today that his government is "prepared to do what is necessary to safeguard our freedom and security" as an emotion-charged debate opened on the deployment of new U.S. nuclear missiles in West Germany.

"Weapons and military strength hold no fascination for us and we are not addicted to rockets," Kohl said in attempting to blunt sharp criticism leveled at him by the opposition Social Democrats, including former chancellor Helmut Schmidt.

More than 150 people were arrested as police clashed with 3,000 demonstrators seeking to disrupt the debate on the deployment of Pershing II missiles on West German soil once parliament has approved the controversial action.

Hundreds of policemen equipped with helmets and shields set up a tight cordon around the parliament building and the Chancellery. Water cannons and tear gas were used to disperse protesters who tried to break through the barriers in an effort to occupy government offices.

The demonstrators paralyzed the capital's main thoroughfares, causing massive traffic jams that stretched several miles. But they failed to thwart the climactic debate that is expected to conclude late Tuesday with a vote to endorse the immediate deployment of the first Pershing II missiles.

Kohl, stressing he "had done all I personally could do" to broker a compromise, said that Soviet insistence at the Geneva arms control talks to retain its monopoly on medium-range missiles meant that West Germany must fulfill its commitments to NATO and proceed to install new rockets to restore a balance of nuclear forces in Europe.

"In a world without peace we must be prepared to do what is necessary to safeguard our freedom and security," Kohl said. "Peace and freedom have their price and everybody must be willing to make the necessary sacrifices. The protection of our freedom now demands that we begin with the stationing of new American intermediate-range nuclear weapons."

Kohl rejected any delay in deployment, saying "The West actually observed a moratorium by not placing a single rocket for four years while the Soviet Union persisted in building up its SS20 missile force even during negotiations."

The chancellor's assertions were challenged by a succession of speakers from the opposition Social Democrats and antimissile Greens party.

Schmidt, making his first speech to the Bundestag, or lower house, since leaving office a year ago, agreed that West Germany must deploy the missiles to prove its reliability as a NATO ally. But he strongly attacked Kohl for lacking the courage or will to prod the Geneva negotiations toward an acceptable agreement.

Turning toward Kohl, Schmidt declared that "your diplomacy should have moved into high gear" when it was revealed that U.S. and Soviet negotiators had reached a tentative compromise known as "the walk in the woods" formula only to have it spurned by their governments in Moscow and Washington.

That plan would have permitted the Soviet Union to retain 75 of the triple-warhead SS20s while the West would deploy 75 cruise missile launchers with four warheads apiece and drop plans to station the rapid, accurate Pershing II ballistic missiles.

Schmidt reiterated that it was "a serious mistake" for the United States and the Soviet Union to reject the formula, which he said was "clearly in German interests."

Schmidt lamented what he described as Kohl's weak and subservient government, contending that West Germany's stature had eroded in the eyes of Moscow and Washington.

"In former chancellor Willy Brandt's time in power and mine, we Germans were the most important partners in dialogue with Moscow," he said. "But all we are today is the most important target for psychological and political pressure" from the Soviet Union.

Other leading members of the Social Democratic Party, which rebuffed Schmidt's personal appeal and voted overwhelmingly at a party congress Saturday to oppose the new missiles, also accused Kohl of feckless leadership and blind fealty toward Washington.

"It is false to say that you have done all that is necessary in order to reach an agreement in Geneva," charged Hans-Jochen Vogel, the Social Democrats' parliamentary leader. "You created an impression in Washington that you were willing to accept almost everything that the present American administration wanted and demanded."

Vogel said the Soviet Union's offer to cut the number of SS20 missiles aimed at Europe from 243 to 140 if the West abandoned deployment plans "was worthy and qualified for negotiation."

But the arrival of new missiles in Western Europe, he warned, will cause the Soviet Union to increase its missile force in Eastern Europe and "tensions that are already dangerous will increase between the two superpowers."

Even more important, Vogel said, is that "the support of our people for the western alliance will decrease because these new nuclear missiles will be stationed here against the will of the German majority."

The opposition charges were rebutted by Foreign Minister Hans-Dietrich Genscher, who said the missile decision is regarded as the litmus test of "where West Germany will stand in the future--as a dependable alliance partner or one that drifts away to neutralism."

"It cannot be denied that our allies are increasingly worried about an incalculable form of German nationalism," Genscher said. "We must counter these worries to maintain stability in Europe."

"This time it is not the strength but the weakness of Germany that creates dangers for Europe," he insisted. "We have bound our identity with the fate of Europe and if we break our responsibilities and attempt to go alone, stability will be lost."

Reuter news service reported the following from Washington:

State Department spokesman John Hughes said there had been no delays or changes in the schedule for deployment of the missiles that calls for "a sequential process" of deploying 572 Pershing II and cruise missiles over five years starting in Britain and West Germany next month.

He would not discuss the precise timetable, but he took issue with a report in The Washington Post Monday that the gap would be as long as nine months between initial deployments in Britain, West Germany and Italy and the next batch sometime in 1984.

The Washington Post report said some West European leaders were pressing Washington to publicize the time lapse between deployments to encourage efforts to reach an agreement to limit missiles.