The government continues to spend billions of dollars less than it wants to, in part because of delays inputting some of President Carter's job creating programs into effect. Congressional Budget Office director Alice Rivlin said yesterday.

Rivlin - who has been critized by some House leaders for hter outspoken, critical alanysis of several Democratic and administration programs - said that because of this spending shortfall her office is not as optimistiv about the economy as is the Carter administration.

"We are somewhat - though not dramatically - more pessimitic than the administration. In general, administraition tend to be more optimistic." She said in testimony before the House Budget Committee.

While the outlook is not as rosy as that painted by the administraion tend to she said that economic conditons have not changed signicificantly enough since Congress passed its tentative 1978 budget last spring to justify a major shift in federal spending policy.

Congressional budget committees begin work on the final, binding 1978 budget next week. Congress must passs the final budget by Sept 15.

Chairman Rep. Robert N. Giamo (D-Conn) sharply critized Rivlin last month for holding a press conference to a budget office study of the President's e energy program will not save the mount of energy he said it would.

There was no criticism of Rivlin at yesterday afternoon's hearing before the House Budget Committee and , in a morning appearance before the Senate Budget Committee, chairman Edmund S. Muskie (D-Maine) warmly paraised her role which he said walked a "line carefully drawn, well drawn" between independent an dpartisan analysis.

Rivlin said lthat her latest estimate is that the gobernment will spemd between $403 bilion and $405 bilion to bilion below Congress's plan last spring and = 1 bilion to $3 bilion below the administration estimates of July 1.

She also said that it appears Congress will spend $5 billion less thanthe $461 billion it set as its spending target for fiscal 1978, which starts Oct. 1

She said that if federal spending falls "much fruther below $455 billion next year, then the budget office's projected gtowth rate for the economy - already more pessimistic than the administraion - would have to be lowere further.

Top administration officials said Yuesday that they expect the economy to growth at a 5 per cent rate for the next 18 months, a pace that will reduce unemployment to 6.6 per cent at the end of 1977 and to 6.1 per cent and 7.2 per cent at the end of this year.

Rivlin said there are a number of reasons why the government does not spemd as much as it wants to, among them overroptimism on the part of some federal agencies about how fast they can spend money for "new programinitiatives and major expansions of existing programs."

Rivlin testified that the job-creating programs proposed by Careter and enlarged by Congress will reduce the unemployment rate by 0.2 percentage points next years