Michael S. Dukakis and George Bush appear to differ more in emphasis than in fundamental approaches to conventional defense questions. Both agree that NATO's defenses must be beefed up to offset the tank-heavy forces of the Soviet-led Warsaw Pact. And both are betting on superior U.S. technology as the key to offsetting Soviet numerical advantages.

They also agree that U.S. allies in Europe and East Asia must begin paying more of the cost of mutual defense efforts. However, neither has endorsed other politicians' calls for draconian cuts in U.S. deployments abroad.Beyond those basic premises, Dukakis complains that the Reagan administration has beggared U.S. programs aimed at offsetting Moscow's 2-to-1 advantage in tanks, slowing production of the M-1 tank and planning to kill production of the Apache missile-armed anti-tank helicopter.

According to Dukakis, some of the money that should have gone for those programs was spent instead on strategic weapons programs that are redundant, like the Midgetman mobile missile, or unworkable, like President Reagan's vision of a "strategic defense initiative" (SDI).

Other funds that should have gone for beefing up NATO's defenses were spent to enlarge from 12 to 15 the Navy's fleet of aircraft carriers, Dukakis says, adding that even Reagan's rapidly expanding defense budgets have not paid for the planes and escort ships the additional carriers would require.

Early in the campaign, Dukakis had said he would block construction of the two carriers intended to complete Reagan's planned naval expansion. But since the contracts for those ships have been signed, he now would pare down the Navy's share of the budget by scrapping the two oldest existing carriers.

Though some critics have dismissed the modern million-dollar tank as a vulnerable dinosaur on the modern battlefield, Dukakis lines up with mainstream Pentagon thinking, pledging to maintain the production rate of M-1 tanks. He also would make it a top priority to develop effective anti-tank weapons.

Thus far, Bush's program for conventional forces has been somewhat less specific. In part, this is because he insists that Dukakis' call for a greater conventional emphasis understates the necessity for modernizing the strategic nuclear deterrent. SDI and modernization of the intercontinental ballistic missile (ICBM) force are needed, in Bush's view, not only to give the Soviets an incentive to negotiate reductions in strategic arms, but also as the ultimate offset to the numerical superiority of Soviet conventional arms.

Bush also endorses a Pentagon policy called "competitive strategies" for drawing up the conventional arms budget. The concept calls for "hitting 'em where they ain't" - investing in high-tech systems designed to exploit structural weaknesses in the Soviet military.

This approach has been applied to the idea of disrupting a Soviet attack on Western Europe by devastating command posts, communications links, supply depots and traffic bottlenecks far behind Soviet lines. To do the job, competitive-strategy proponents advocate swarms of "stealth" fighter jets, designed to evade enemy radars, and long-range conventionally armed cruise missiles.