The Republican budget proposal passed by the House last week contains steep budget cuts for the Federal Trade Commission--even sharper than those called for by President Reagan earlier this year.

Under the GOP plan, the FTC's funding for fiscal 1983 would be slashed to $47 million--$24 million less than the current budget and $14 million less than Reagan sought.

The proposed cut represents a significant congressional swipe at the already embattled FTC because it appears to be the only one for a regulatory agency that is steeper than those asked by the administration.

The $24 million reduction is only a proposal in the GOP House budget; a real cutback would require action by the two appropriations committees and the full House and Senate. The assumption was made, however, as part of the deliberations of the administration and the House Republican leadership, which agreed to it when formulating the measure that passed by a vote of 220 to 207.

If upheld, "It could have a devastating effect on the commission, especially on its Bureau of Competition," which investigates antitrust violations, charged Rep. Neal Smith (D-Iowa.), the chairman of the House appropriations subcommittee that sets funding levels for the FTC.

Smith and FTC officials were caught off guard by the budget proposal. Nonetheless, after careful review, FTC officials said that, for the moment at least, they are not alarmed by the action.

For one thing, they noted that the proposal well could be altered in the current House-Senate conference committee when measured against the Senate-set $71 million funding level for the FTC for fiscal 1983.

What's more, they added that, even if the proposal remains unchanged, it is not binding on the appropriations committees.

Even so, Smith, a strong FTC supporter, was clearly concerned by the proposal. Although the proposal is not binding, he said that, if his subcommittee gave the agency more money, it would have to cut money from somewhere else. "When this budget is so lean, it will be very difficult to shift funds from anywhere else," he said.

Smith suggested that the budget-cut proposal must have been written by the Office of Management and Budget, which last year tried unsuccessfully to reduce the FTC's budget by closing the agency's Bureau of Competition. Stiff congressional opposition stifled that move.

OMB officials said it was unclear where the proposal originated. However, a top Republican staff aide said the cut was made because of "major philosophical differences between Congress and the agency on appropriate agency issues."

For the past four years, Congress has attacked the FTC for overstepping its legal authority and has placed a series of curbs on the agency's powers.