President Reagan, facing an increasingly hostile Congress, today took his case for a continued military buildup to an enthusiatic audience of 3,700 Marine recruits who roared their approval of his program.

"I'd like to take some of those people in Washington who are always trying to cut defense spending and bring them here to Parris Island," said Reagan, who is seeking to raise defense spending by 11 percent to $320 billion. "To all of those who say we must always cut defense first, that America can't afford a strong military, I have just one thing to say: Tell it to the Marines."

Both the House and Senate budget proposals would slow the major military spending buildup that has been taking place during the five years Reagan has held the presidency. The House would set the Defense Department budget at $285 billion and the Senate would provide $301 billion.

In addition to pressure on Congress to reduce the deficit, Reagan's plans to abandon the terms of the SALT II strategic arms limitation treaty have provoked threats to cut spending for key administration programs, including the Strategic Defense Initiative (SDI), or "Star Wars," space-based defense against intercontinental ballistic missles.

To dramatize his appeal for the military, Reagan watched recruits perform on the "confidence course" here, including an obstacle called "the tough one," where recruits slid down a 40-foot rope, climbed over 12-foot high parallel bars and then crawled on three ropes suspended 14 feet over a pool of muddy water. Two recruits failed to make the crossing, yelling "Marine Corps" just before letting go of the ropes.

Marines are strong backers of the Reagan military buildup, and they voted for Reagan's reelection by large margins, according to polls. "I know who I voted for," Staff Sgt. Michael Hudlund, a drill instructor, told reporters. "I think Reagan's a great man."

The president got a warm and characteristic reply to his praise of the Marines and the defense buildup. The recruits, along with 4,000 base personnel, their families and friends, gave the Marine cheer, a grunting noise which one Marine Corps public relations official said is spelled "arruugah" while another said it is "arruuugaaahh."

Later in the day, Reagan resumed what has been a sustained effort to raise money for Republican Senate candidates, appearing at a $500-a-plate luncheon for the North Carolina GOP Senate nominee, Rep. James T. Broyhill, in Greensboro.

The gathering, which promoters claimed was the most successful fund-raiser in the state's history, grossed $620,000 and was aimed at healing wounds in a local GOP that just experienced a bitter Senate nomination contest. Broyhill's defeated Republican Senate primary opponent, David Funderbunk, did not attend.

Broyhill faces former governor Terry Sanford in the Nov. 4 contest to succeed Sen. John P. East (R-N.C.), who is retiring after one six-year term.

Broyhill has not always agreed with the president on major issues and only last week defied Reagan in voting for a Democratic trade bill, a conflict the president indirectly acknowledged in his speech:

"We may not always see eye to eye but we have the same desire -- to make life better for the people of our country . . . Jim and I know American workers can outwork, outproduce, and outcompete anybody in the world."