President Reagan's nationally televised appeal for his defense spending proposals ran head-on into a deeply ingrained public attitude that the military buildup under his administration has involved a large amount of waste and should be slowed, congressional leaders said yesterday.

As a result, they said, Reagan's speech Wednesday night seeking to drum up popular support for more defense spending appeared to have little initial impact in Congress, where the administration faces a fight to prevent the Pentagon budget from being cut.

Congressional offices reported a much lower than normal flow of telephone calls and messages following a presidential address, with the results in many cases running counter to Reagan's goal. The office of Sen. Arlen Specter (R-Pa.) reported getting 41 calls by 3 p.m. yesterday, all of them opposing further defense spending increases.

Rep. C.W. (Bill) Young (R-Fla.), a member of the Appropriations subcommittee on defense, said his office received about 100 calls, with two-thirds supporting the president. But, Young added, "I don't know that that speech is going to change a lot of minds in Congress," which remains preoccupied with deficit reduction and with the uncertainties of the Gramm-Rudman-Hollings balanced-budget law.

Democrats were quick to brush aside the Reagan appeal. "I don't think he sent out any flaming message," House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said.

That assessment was shared by many Republicans who support the Reagan defense buildup but who repeatedly cited reports of a $600 military toilet seat as a symbol for what they said has undercut public as well as congressional backing for the program.

"It's gone," Rep. Dick Cheney (R-Wyo.), the chairman of the House Republican Policy Committee, said of the broad support the president once enjoyed on defense spending.

Cheney said this was due to several factors, including a perception that the defense buildup has gone far enough and "all the allegations about $600 toilet seats, which have been devastating to popular support."

"He's right on the merits," Cheney said. "But it's going to be awfully difficult to get approval through Congress for significant increases in defense spending."

Republican leaders had urged Reagan to make the speech. Yesterday, GOP lawmakers said it will take much more than one speech to salvage anything close to the 8 percent real increase, above the rate of inflation, that Reagan has proposed for the Defense Department in fiscal 1987.

"It will help some, but it's not enough by itself," House Minority Whip Trent Lott (R-Miss.) said. "It's going to take a real drumbeat."

Lott said that, while he favored the 8 percent real increase in defense spending, the "absolute best" that a majority of House Republicans would now support would be 2 percent above the inflation rate.

"It's not just liberal Democrats, but a lot of conservative Republicans who are saying we want our money spent carefully," Lott said after citing the toilet seat reports and other alleged cases of waste and fraud in Pentagon spending.

Rep. William L. Dickinson (Ala.), the ranking Republican on the House Armed Services Committee, said he will fight for a 3 percent real increase in defense spending. He would like more, Dickinson said, but "in today's political climate it's just not there."

Without solid backing from members of his own party, Reagan's defense budget request faces virtually no chance of approval in Congress and may be threatened by cuts from current spending levels.

In the House, some GOP lawmakers such as Rep. Connie Mack III (Fla.) are already saying they are willing to accept "zero real growth" in defense spending that would keep pace with but not exceed the inflation rate.

Mack, one of the leaders of the younger conservatives among House Republicans, said he would favor this rather than a tax increase to continue the defense buildup.

In addition to the waste issue that has undercut Reagan's support on defense spending, congressional leaders said the president is bucking a new political psychology that has developed under the balanced-budget law. That law calls for automatic cuts, 50 percent from defense spending and 50 percent from domestic spending, if Congress does not meet yearly defict targets leading to a balanced budget by fiscal 1991.

House Majority Whip Thomas S. Foley (D-Wash.) and Armed Services Committee Chairman Les Aspin (D-Wis.) have been arguing for weeks that this formula of equal sharing of cuts between defense and domestic spending is likely to shape whatever budget emerges from Congress this year.

"I think we will probably have to proceed with something like a freeze" in defense spending, Foley said yesterday.

Mack, who predicted earlier this week that Reagan's speech "is not going to change the numbers coming out of here," said, "The whole concept that has developed is that if we are going to freeze programs, that means defense, too."

Aspin said that by endorsing the balanced-budget law, Reagan had doomed any chance for a defense spending increase next year.

"If the president says he will veto a tax hike and that the only way to reduce the deficit is to cut spending, then there is no way on God's green earth that defense will emerge from this exercise unscathed," he said.