One of Ronald Reagan's chief budget advisers said yesterday that liberals and blacks should not be alarmed at the propsect of large-scale spending cuts under a Reagan administration, and suggested that in some cases the poor may actually wind up receiving more once some programs are revamped.

Casper W. Weinberger, a former Nixon administration budget director who is leading Reagan's search for spending cuts, flatly dismissed suggestions that the new administration might slash the Head Start program, for example, saying he considered that a program that "can do a lot of good." Asked for examples of what cuts Reagan might recommend, he cited excessive travel by government officials.

Weinberger declined to provide any specifics on what cuts the president-elect is considering. And he said Reagan still stands "absolutely firm" on his pledge for a 30 percent tax cut over three years, even though critics fear it would be inflationary.

Weinberger's remarks on "Issues and Answers" (ABE, WJLA) did not add significantly to the little the Reagan camp has disclosed so far about which programs the president-elect is planning to cut. Details are not expected until after Reagan takes office.

Weinberger alluded repeatedly to Reagan's efforts as governor to revamp California's welfare program. He said Reagan made "substanatial changes in the welfare program, but the money saved, a large part of it, went to improve and increase the benefits . . . ."

Reagan has set a "minimum" goal of trimming projected fiscal 1981 spending levels by 2 percent or more -- a move that would cut outlays at least $13 billion below the $632 billion forecast in Congress' latest budget resolution. Weinberger reaffirmed yesterday that he'd like to cut more, if possible.

However, he listed only a handful of general areas for possible cuts -- part of $2 billion in Medicare fraud estimated recently in a House subcommittee study, some of the $8.9 billion the government spends each year on travel, and elimination of duplication in some welfare programs.

Asked about fears by blacks and liberals that the cuts might hurt the poor, Weinberger said that both he and Reagan were "distressed" by that image and that there was "no basis" from Reagan's record as governor to suggest any such thing.

"There is no man who is more concerned with the welfare and human condition of everybody . . . then Gov. Reagan, and certainly there isn't the slightest evidence of any activity . . . during his eight years as governor that would give rise to suspicions or worries of that kind," Weinberger said.

Weingberger's remarks were regarded as optimistic by some analysts. With defense outlays rising sharply and interest rates on the way up, many experts believe Reagan will have to concentrate most of his cuts in the area of social programs if he is to meet his $13 billion goal.

The budget adviser also reiterated his opposition to using general income tax revenues to finance Social Security benefits, and said Reagan would not seek to raise the retirement age as a budgetry move -- though he said the retirement age might be increased later if older persons demand it.