BONN, DEC. 21 -- The West German government has officially reduced its forecast for economic growth in 1988 and has blamed the revision on the recent plunge in the dollar's value.

In a related move, Chancellor Helmut Kohl appealed today to the United States to do more to prop up the dollar. Kohl again rejected suggestions that West Germany could act as a "locomotive" to help lead Europe and the world to more robust economic growth.

Finance Minister Gerhard Stoltenberg, in an interview published Sunday, said that West Germany "must prepare" for real economic growth of between 1.5 percent and 2 percent in 1988. That is down from the government's earlier predictions for real, or inflation-adjusted, growth of between 2.25 percent and 2.5 percent next year.

The reduced forecast was likely to fuel U.S. government charges that Bonn is not doing enough to promote economic growth and fight world trade imbalances.

Stoltenberg's forecast represented an implicit admission that West German growth measures announced at the start of this month was insufficient to raise 1988 growth significantly from the expected rate for 1987 of between 1.5 percent and 1.7 percent.

The statements by Stoltenberg and Kohl appeared designed to outline West Germany's positions on international economic policy in advance of the expected release soon of a joint declaration by the seven leading western industrialized nations in the Group of Seven.

Kohl's chief spokesman, Friedhelm Ost, confirmed today that the G-7 nations planned to issue a statement renewing the commitment to international cooperation to support the dollar and otherwise coordinate economic policies. Ost said that the date for releasing the declaration was "open;" it is expected the statement will be released after the U.S. Congress passes its budget-reduction package and President Reagan signs it.

Stoltenberg's growth forecast for 1988, even after the downward revision, was more optimistic than many private predictions. The Institute of the German Economy, which is linked to the Confederation of German Industry, forecast last week that growth next year would be 0.75 percent, down from the 1.5 percent that it estimated for 1987.

In a new twist in the long dispute between U.S. and West German policymakers, Stoltenberg placed almost all of the blame for the worsening of West Germany's growth prospects on the recent fall in the U.S. dollar.

He argued that the dollar's drop, by raising prices of West German products in foreign markets, would reduce growth by cutting into West German exports.

Given West Germany's repeated complaints that Washington was doing too little to support the dollar, Stoltenberg's comments amounted to an effort to blame the United States for his nation's gloomier growth outlook.

"The decisive reason for the slower growth is the drastic changes on the currency markets," Stoltenberg said in an interview with the weekly newspaper Welt am Sonntag.

Stoltenberg added that he believed that the fall in the dollar "has already gone too far." He said that West German exporters "could work profitably" if the dollar were worth between 1.8 marks and 2.1 marks. The dollar was worth 1.634 marks at the close of European trading today.

{Later in New York, the dollar closed at 1.6280 West German marks. The dollar ended at 126.70 yen in New York, down from 127.05 yen Friday. Earlier in Tokyo, it strengthened slightly to 126.65 yen from its post-World War II record low closing of 126.45 yen on Friday.}

The United States has asserted that West German growth is sluggish because the government has been too afraid of inflation to adopt adequately expansionary policies. The United States contends that faster West German growth would spur economies throughout western Europe, and that the Europeans then would import more U.S. products and help narrow the gaping U.S. trade deficit.

The U.S. administration has been especially forceful in pressing Bonn to move forward some or all of a package of tax cuts scheduled for 1990. Tax cuts totaling about $8.5 billion already are scheduled to take effect on Jan. 1, 1988, but the United States and many West German analysts contend that this is not enough.

Stoltenberg reaffirmed in the interview that the 1990 tax cut would not be enacted earlier. He said that the necessary approval could not be obtained from the governments of West Germany's 10 states, which must give their assent to any tax changes.

In a similar vein, Kohl said in an interview published in today's Die Welt newspaper that West Germans "must not overestimate our capacity" for helping the world economy.

Asked how he answered critics who said that West Germany should be an economic "locomotive," Kohl said that a previous experiment with such a policy in the late 1970s had "negative effects."