West Germany's largest political party, in an apparent attempt to soften its hard-line image, is inching toward a new assessment of relations with the Soviet Bloc.

Talk of a shift in the East-West stance of the Christian Democrats is still a controversial issue in the party, which has been a traditional fountain of West German anticommunist and pro-U.S. sentiments.

Christian Democratic Union chairman Helmut Kohl, for one, strongly allergic to anything that would disturb his party's normally placid demeanor, has brusquely argued against the need for a change in policy toward the Communists and will probably say as much if asked about the subject during a visit to Washington this week.

But appeals for a change in the party's conservative tone can be heard from powerful CDU figures, including the party's general secretary Heiner Geissler, CDU deputy chairman Kurt Biedenkopf and the party's parliamentary group deputy chairman Leisler Kiep, who, along with many others, expect their party to come to power in Bonn before too long.

Behind their call is certainly no new-found love for the Soviets, but rather a tough political judgment that the CDU must portray itself as a dynamic, rather than reactionary successor to the government of Chancellor Helmut Schmidt. Implicit in this tack is an acknowledgement that West Germany's commitment to detente, fostered during the past dozen years of Social Democratic rule in Bonn, is irreversible and could not be refuted or ignored by a future conservative government here.

The motions for a CDU policy review occur also against the turbulent backdrop of grass-roots opposition to Atlantic Alliance nuclear missile plans. This opposition contains a strong feeling of estrangement from the United States.

It can be argued, as some leading CDU members do, that the party, no matter how it might have to temper its conservatism if it resumes power in the 1984 national elections or sooner, need not make any gestures yet toward the left. This view holds that the self-flagellating fit that has been tearing apart Schmidt's Social Democrats and undercutting the chancellor's leadership may be enough to hand the opposition party the reigns of government without requiring much of an effort.

Recent polls suggest the Christian Democrats, to attain power, may not even have to consider an eventual coalition arrangement with the Free Democrats, the centrist junior coalition partner in the current government. Public support for the CDU has been running about 50 percent, which is several percentage points above the party's historical average.

But the number of disenchanted voters fleeing the Social Democratic Party (SPD) is substantially larger than the gains recorded for the CDU. This has given further strength to those who advocate that the CDU be made to appear more sensitive to controversial topics, particularly those that preoccupy West Germany's more pacifist, neutralist-inclined youth.

As part of a grand coalition with the Social Democrats in the mid-1960s, the Christian Democrats actually helped to initiate West Germany's move toward accommodation with Eastern Europe and the Soviet Union. But the demands then of the CDU's right wing prevented the party from probing in depth the Communists' terms for an adjustment in relations. It took a new Social Democratic-Free Democratic coalition under Willy Brandt to negotiate the treaties with Moscow, East Berlin and Warsaw that marked Bonn's breakthrough to the East.

The CDU sharply attacked Brandt's initiatives at the time. In recent years the party's Eastern policy has consisted largely of a tight-lipped pledge that existing West German treaties with the Communists would be kept, with little more said to suggest that a CDU government would pursue new agreements.

Such rigidity allowed the Social Democrats to scare voters into thinking during last year's general elections that if the Christian Democrats took power, the nation's already disturbed sense of peace with the Communists would be ruptured altogether.

Signaling a desired shift toward a more open, compromising image, CDU General Secretary Geissler said recently, "We don't have only conflicting interests with the Soviets, we also have common interests." About the treaties, he added, "We must fill them with life."

Meantime, the CDU's Kiep is preparing for a trip to Moscow later this month in what has been billed by some party officials as a step toward regular exchanges of opinion between the Christian Democrats and Kremlin leaders.

Contributing to the new portrayal of the party as no spoiler of detente was this year's West Berlin election, which routed the Social Democrats from city hall for the first time since World War II and installed a CDU government in a city that is one of the focal points for Bonn's Eastern policy.

The new mayor, Richard von Weizsaecker, sounded a willingness in his inaugural speech in August to continue to deal with the Communists on the other side of the wall. He voiced disappointment at the recent stagnation in East-West relations and spoke invitingly of "peaceful development" in East-West negotiations on concrete topics.

Then last week, on a day when most of the seats in West Germany's parliament were empty on the assumption that another boring debate on inner-German relations was about to take place, a CDU spokesman made an offer to the Schmidt government that made front-page news here.