Despite increasingly strong objections from the Soviet Union, both Norway and Denmark are actively considering stockpiling American tanks, artillery and other heavy equipment to speed the reinforcement of NATO's northern flank with U.S. Marines in a military crisis.

Discussions between Norwegian and Danish military officials and their American counterparts in NATO have been going on for some time, in response to the steady buildup of Soviet air, sea and land forces in the north.

Under agreements already negotiated, the Norwegians and Danes will store in depots at some of their air bases sizable amounts of fuel, maintenance equipment and ammunition for use by American and other allied planes in an emergency.

Only since the Soviet invasion of Afghanistan, however, has the United States informed Norway and Denmark that it will have ready for negotiation this summer detailed proposals for stockpiling heavy weapons, tanks and other vehicles for tens of thousands of U.S. troops that would be airlifted into the two countries if they were threatened with a Soviet attack.

Earlier this week, at the end of 10 days of large-scale, cold-weather NATO maneuvers in northern Norway, Gen. Bernard Rogers, supreme allied commander in Europe, said the stockpiling and rapid reinforcement plan was necessary to improve allied reaction time in a conflict on NATO's northern flank, which controls vital sea lanes from the Soviet Union and Eastern Europe into the North Atlantic.

At a press conference after the "Anorak Express" exercises above the Arctic Circle, in which about 20,000 troops from the United States and other NATO nations took part, Rogers said he was "satisfied that we are ready, but not satisfied that we can bring the reinforcements to north Norway as rapidly as needed."

Subject to final negotiations over the precise weapons and other equipment in the U.S. proposal and its financing, Norway is likely to agree to stockpiling and rapid reinforcement plan. Norwegian military officials have long been on record as seeking a strong NATO reinforcement commitment to improve the credibility of their own defenses against possible attack across the 120-mile border with the Soviet Union.

Denmark, however, cannot negotiate much further with Washington until the stockpiling plan is submitted to uncertain internal negotiations within the minority government of Social Democratic Prime Minister Anker Jorgensen and the Danish parliament.

Left-wing Danish opponents of both the stockpiling plan and the agreement to store fuel and ammunition for NATO planes at Denmark's Karup Air Base contend that these constitute a departure from the polices of Denmark and Norway since joining NATO that neither foreign troops nor nuclear weapons would be based on their soil in peacetime. The critics charge that foreign troops could accompany the stockpiled military equipment and that the weapons and planes could easily be armed later with nuclear weapons.

Similar charges have been made repeatedly in recent weeks by the Soviet press, which stepped up its attacks on Norway in particular before the "Anorak Express" exercises there.

"Norway's transformation into an arsenal of foreign offensive weapons openly aimed at the Soviet Union cannot be described otherwise," the Communist Party daily Pravda argued last month, "Than as a departure of the government from the principles of its own declared policy of not stationing foreign troops or nuclear weapons on Norwegian soil in times of peace."

Norwegian officials responded by insisting that the voluntary nuclear ban would be observed, that Norwegian personnel would handle the stockpiled equipment and that the point of the stockpiling plan was to avoid having to ask NATO forces to come to Norway's assistance any earlier than absolutely necessary in a crisis.

But here in Denmark, Defense Minister Paul Sogaard said in an interview that the rapid reinforcement plan involves the possibility of U.S. Marines or other NATO troops arriving in Denmark before war actually began if an attack appeared imminent or a serious crisis built up.

Acknowledging that this would mean a modification of Danish policy, Sogaard called it "a political question" that required "a political decision" by the Social Democratic government and the rest of parliament, where the Danes traditionally seek broad consensus of defense policy.

Sogaard said he believes, however, in light of the present situation that "the Danish people now have more understanding of the need" for a contingency defense strategy involving NATO equipment stockpiling and rapid reinforcement. He noted that weapons and equipment already are stored along the Danish-West German border on the Jutland Peninsula for use by West German troops in time of war. Other government officials here pointed out that Danes continued to support NATO membership by more than 2-to-1 in opinion polls.

But unlike the similarly left-of-center, labor union-based government in Norway, Jorgensen's Social Democrats hold only 69 of the 179 seats in the Danish parliament and must seek the support of their own often rebellious left wing plus some of the nine other parties in parliament on important defense and economic issues.

To win the left wing's support for cuts in the government's welfare state spending and other austerity measures proposed to rescue Denmark's steadily deteriorating economy, Jorgensen has had to compromise on defense issues. This led to Denmark's attempt to delay the NATO decision to modernize its tactical nuclear weapons in Europe, even though none of them would be deployed in Denmark or Norway.

Since then, in the parliamentary negotiations for a new four-year national defense policy to take effect in 1981, Denmark's Social Democrats proposed that the defense budget be held down along with the rest of public spending. This proposal has been criticized strongly by U.S. and NATO officials and by the Danish right-of-center opposition parties, who are seeking at least the 3 percent defense spending increase recommended by NATO and publicly agreed to by Jorgensen in the past.

Officials here now say Jorgensen's proposal of "zero growth" in defense spending was only an opening bargaining position designed to produce a compromise increase of perhaps 2 percent after the expected uproar over the coming cuts in social services has died down.

"We must take care of our economic situation first," Defense Minister Sogaard said. "If we are going to cut down on social welfare, on education and a lot of other things, then we cannot increase defense spending by 3 percent or more. It's not politically possible. It could split the party and the country."

Sogaard said Danish defense officials have studied ways to trim waste from the military without reducing its capabilities.