Defense Secretary Caspar W. Weinberger lashed out at congressional conferees yesterday, charging that their proposed moratorium on further testing of antisatellite weapons would give the Soviet Union "life-or-death veto power" over the U.S. program and waste $20 million spent by the Pentagon last week in launching test targets.

But congressional sources said there was no sign of White House lobbying to overturn the proposed ban. President Reagan also reportedly told a key senator that he would not try to reopen the antisatellite (ASAT) issue if Congress voted to resume production of chemical weapons, which the conferees have done.

The ban, passed by House-Senate conferees last Friday and approved yesterday by appropriations committees in both chambers, deletes funds in fiscal 1986 for flight testing of missiles against an object in space unless the president certifies that the Soviet Union has resumed testing of such weapons.

Pentagon spokesman Robert B. Sims, reading a statement approved by Weinberger, said a ban on testing a satellite-killer missile could "undercut arms control, impair our national security and waste money."

Sims said the Soviets have an "operational" antisatellite system that poses a "growing threat" to U.S. satellites. Moscow would have no motivation to negotiate a ban on the weapons if the U.S. program is canceled or curtailed, he added.

"This action places the future of the U.S. ASAT program in Soviet hands," Sims said. "They have already proven the effectiveness of their system, so they do not require additional testing."

Sims, responding to questions, said a moratorium would waste the $20 million spent to launch two satellites last Thursday as test targets because the batteries powering their testing mechanism would expire before the next fiscal year begins in October.

The Air Force had planned two antisatellite tests in 1986 against inflated balloon targets released by the satellites launched last Thursday. The first U.S. test in September destroyed an old scientific satellite over the Pacific in what experts said displayed a capability far surpassing that of the Soviet Union.

Asked why the Pentagon sent up test targets last week before the funding issue had been resolved in Congress, Sims said the launch had been scheduled in advance and "there are certain windows which scientists have to meet."

He said although Pentagon officials knew that Congress was still debating the issue, they did not envision "this dramatic a move." Conferees, seeking to prevent the administration from using test funds left over from last year, drafted language shutting off funds in the fiscal 1986 defense bill "or any other act."

Rep. Les AuCoin (D-Ore.), a House conferee and sponsor of the moratorium amendment, called Sims' explanation "baloney." He said Thursday's launch was intended to apply pressure as conferees were debating whether to finance missile shots against the targets.

Even though Congress had earlier authorized two more antisatellite tests this year, AuCoin said, "any open-minded observer" would have known of the strong sentiment in the House against voting funds for the tests this year.

AuCoin said a moratorium will improve U.S. security by giving the Soviets an incentive not to develop weapons that would threaten U.S. satellites.

Sims said Weinberger's statement reflected the president's views, and White House spokesman Larry Speakes told reporters that Reagan has "problems" with the moratorium.

"It would be the wrong signal to send to the Soviet Union when we have an opportunity to make progress in the arms-control area," he said.

But Reagan, in a telephone call to Sen. Mark O. Hatfield (R-Ore.), chairman of the conference committee, said he would not reopen the ASAT testing issue if Congress went along with another decision of the conferees to allow production of chemical artillery shells in 1987, according to congressional sources.