The Republican Party today opens its attack on President Carter's defense program, calling it "over-conciliatory and under-competitive."

Robert Ellsworth, an assistant secretary of defense under President Ford, wrote a critique of Carter's fiscal 1979 defense budget for the Republican National Committee.

In the Ellsworth draft expected to be made public today Carter is accused of having "a strong predisposition to unilateral American self-denial" in the field of strategic weapons.

Specifically, the Republican Party faults Carter for canceling production of the B1 bomber, failing to put the MX intercontinental ballistic missile into full-scale development, and cutting back on Navy shipbuilding to a "shocking" extent.

The paper argues that the bomber was canceled before it was demonstrated that the cruise missile "could ever be a high-confidence substitute" and "without gaining any concession whatsover" from the Soviets in current arms control negotiations.

"In the U.S. Soviet military relationship," the Republican paper claims, "the Carter administration has been over-conciliatory and under-competitive." The paper calls for a "new direction" for Carter administration defense policies.

The Republican attack comes against the backdrop of a farewell statement from Air Force Gen. George S. Brown expressing some of the same concerns about the United States losing its military edge to the Soviet Union, Brown, chairman of the Joint Chiefts of Staff who is scheduled to retire this summer, told Congress in a posture statement to be discussed by the Senate Armed Services Committee today: "In looking back over my previous reports to you. I am struck by the fact that in nearly every area of military strength there has been a relative decline over the years in relation to the Soviet Union."

Although Brown said the United States had increased its military strength over the last several years, he added that "in light of the extent of growth in the military capabilities of the Soviet Union, it is questionable whether what has been done is enough to assure the security and well-being of our country in the coming years."

The nation's top-ranking military officer said there was no quick way to solve the problems he sees, given the time it takes to develop new weapons and limits on funds, and "thus the military risk to the nation - already relatively high - will increase."

Brown said that the Soviet Union appears to be obtaining the means "both conventional and nuclear, not only to fight and survive war, but to emerge the stronger side as well."

He said that "U.S. development and deployment of modern strategic weapons are not keeping pace with the Soviet Union. The current U.S. bomber force will require modernization beyond mounting the cruise missile" on the plyanes.

Brown, in his 124-page posture statement reflecting the collective view of the joint Chiefs of Staff, stopped short of dissenting from the Carter administration on the fiscal 1979 budget that calls for $126 billion for weapons and troops. But the chiefs' warnings are expected to be cited by hawkish members of Congress as they assess the new Pentagon budget over the next months.