President Reagan, trying to demonstrate that he is still a political force, threatened yesterday to use his veto power repeatedly to block major domestic legislation expected to win approval from the Democratic-controlled Congress.

White House spokesman Marlin Fitzwater said Reagan would veto a banking bill that includes a savings and loan bailout, an omnibus trade bill and a catastrophic-illness insurance measure if they reached him in their present forms.

"The president looks forward to the skirmish," Fitzwater said. "The Democrats are trying to force big spending bills on us, and he's ready to take them on."

Fitzwater said Reagan made his views known yesterday morning at a meeting with Republican congressional leaders. According to participants, the president was in a combative mood and made it clear he does not intend to back away from his legislative agenda because of damage inflicted by the Iran-contra scandal.

While Fitzwater specified only three measures, other White House officials said at least eight major bills and several minor ones face vetoes. Among them are a housing bill now in Senate-House conference and a defense authorization bill pending in the Senate that would restrict development of Reagan's missile-defense plan, the Strategic Defense Initiative.

White House officials expressed confidence that Congress would sustain vetoes of most of these measures despite stinging overrides earlier this year on water-cleanup and highway-construction measures. Fitzwater said there was "a far better chance" of sustaining vetoes on the three pending measures Reagan objected to in his meeting with GOP leaders yesterday.

But differing views were expressed within the White House over the wisdom of a broad-scale veto strategy. One official said the president needs to use the veto selectively and can demonstrate convincingly that he "is no lame duck" by having vetoes upheld.

Another White House official said Reagan is determined to veto any measure he considers a "budget buster" regardless of the political prospects of upholding a veto. Reagan decided to veto the highway bill earlier this year despite the warning of White House chief of staff Howard H. Baker Jr. that it was likely to be overridden.

Of the measures discussed by Fitzwater yesterday, only the banking bill is considered likely to reach the president's desk before the August congressional recess. Using words similar to those of Treasury Secretary James A. Baker III, Fitzwater called this measure "a very bad bill, unacceptable in every respect, {that} reverses and undercuts all the deregulation efforts the president has taken in regard to financial services in the past 6 1/2 years."

Fitzwater quoted Reagan as saying to the Republican congressional leaders, "One thing is clear: We are faced with a major Medicare expansion bill under cover of being called a catastrophic-insurance plan for the elderly." Reagan said it would add $8 billion to the deficit by the year 2000.

The president also was quoted as saying that it was up to the Democratic leaders of Congress to send him a trade bill he could sign. "So far, the signs point straight to veto on this bill," Reagan said.

Sen. Bob Packwood (R-Ore.) told the president he believed a veto of the trade bill could be sustained, Fitzwater said.