Senate Republicans yesterday turned back a series of Democratic amendments to a record $208.3 billion military spending bill, setting the stage for a funding victory for President Reagan on his proposed B1 and MX weapons systems.

One amendment offered by Senate Minority Leader Robert C. Byrd (D-W.Va.) to add $250 million for the Stealth bomber was tabled, 51 to 40; another proposal by Sen. Carl Levin (D-Mich.) to spend $220 million on four KC10A refueling tanker airplanes was defeated, 55 to 38.

The amendments were part of a two-stage Democratic strategy to increase funding for various weapons systems and then propose to pay for them by deleting money from the B1 or MX programs.

"This is the beginning of the B1 battle," said Sen. Ted Stevens (R-Alaska), chairman of the Senate defense appropriations subcommittee and floor manager of the military spending bill. "It is one of the most delightful strategic tactics I've seen in a long time and it's going to put me in a position of voting against the KC10A even though I'm in favor of the KC10A."

Stevens was hardest pressed to keep his troops in line against Byrd's proposal to increase money for the popular Stealth, which is to be the nation's advanced technology manned bomber for the 1990s. Byrd, arguing that the administration's plan to build 100 B1 bombers could cool its enthusiasm for rapid development of the Stealth, proposed to add $250 million in research money for fiscal 1982 to bring the funding level for the Stealth up to the figure already approved by the House.

Stevens countered that there was a limit to the amount of money that could be spent at this stage in the research on the bomber, and he assured his Democratic colleagues that the administration remained committed to building the Stealth as quickly as possible.

A Democratic staff member said yesterday that the defeat on the preliminary amendments had been expected and that opponents of the B1 and MX would do no better when the debate on those systems reaches the floor today.

"We are going to attempt to win the debate even if we lose the issue," said the staff member, who asked not to be identified. "If we bring together a good percentage of the Democrats, then we think we're creating a recognition that the party has a position on these strategic questions."