President Reagan Wednesday vetoed a $299.5 billion defense authorization bill for the next fiscal year, saying it would return the United States to the course of "weakness and accommodation of the 1970s."

Reagan announced his decision during an appearance in the White House briefing room. Vice President George Bush and leading Republicans had urged Reagan to reject the legislation.The bill essentially would have authorized the spending levels the administration sought, but it sought to rearrange defense spending priorities. Administration officials complained that the legislation contained language that would have tied the president's hands on future arms control negotiations with the Soviet Union.

Defense Secretary Frank C. Carlucci had supported the bill, however.

Citing progress he said is being made in East-West relations and in settling regional conflicts, the president said, "Over time, the defense bill that I have just vetoed would have placed in jeopardy all of these diplomatic and strategic advances.

"It would endanger progress in arms negotiations by giving away all of our leverage without getting a single thing in return from the Soviets," he said.

He said the bill, if it became law, would also "cripple the very concept of a space shield against nuclear attack (the Strategic Defense Initiative program), and I will not abide this."

"They say this bill would take the stars out of Star Wars," he said. "With my veto today, I am putting back the `I', initiative, in SDI."

Reagan disavowed political motives, saying: "I can be patient no longer. Congress needs to get to work and come back with a bill I can sign. These are issues of national security, and they must remain above partisan politics."

On Capitol Hill, Sen. Edward M. Kennedy, D-Mass., criticized the president's action and said "it would be a travesty now for the president to start playing presidential politics" with the nation's defense.

Kennedy said the bill had been the result of bipartisan compromise. "These compromises reflected the good-faith efforts of Congress and the president."

The veto may be difficult to override, particularly in the House. The bill was passed July 14 by both the House and Senate, and the votes in both Democratic-controlled chambers generally went along party lines.

The House vote was 229-183 and the Senate tally was 64-30. A successful veto override would require a two-thirds margin in each chamber.