The White House warned Republican House members yesterday that the GOP will suffer politically if they fail to support a tax overhaul bill, and key Republicans acknowledged that combined pressure from President Reagan and Democratic leaders is having an effect.

House Republican leaders remained unanimously opposed to the Democratic version of tax revision, and some told the president so in colorful language. "I told him, 'Mr. President, if you're going to lie down with the dogs, you're going to get fleas,' " said Minority Whip Trent Lott (R-Miss.). "I got a chuckle out of him."

But Democratic leaders predicted their version will be approved this week. And some GOP strategists privately agreed.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) told reporters he thinks the bill will pass, and administration and GOP strategists said they believe that House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) will find enough votes to win on the floor, even though he does not have those votes yet.

O'Neill said the Democrats could probably get 50 Republican votes for their tax package, but Lott said closer to 25 to 30 GOP legislators were leaning toward the Democratic bill over an alternative Republican tax package. About 30 more were undecided, Lott said.

White House officials said they do not have a firm head count.

The president has said he does not like the Democratic version of the bill, but wants it passed and sent to the Senate to keep the process moving.

Reagan's telephone calls to GOP House members fell flat in at least a few cases. He called Lott, for example, just as Lott was on another line with White House legislative liaison M.B. Oglesby telling him it was useless to have the president call because he was adamantly opposed to the Democratic bill.

Calls to Reps. Jack Kemp (R-N.Y.) and Dick Cheney (R-Wyo.), both members of the GOP leadership, also failed, aides to the legislators said. Rep. Guy Vander Jagt (R-Mich.) said he told White House representatives not to have the president call because his mind already was made up. Reagan did not call Minority Leader Robert H. Michel (Ill.) because Michel has said openly that he opposes the Democratic legislation, officials said.

Reagan has encouraged legislators to support a Republican alternative plan if they wish, then vote for the Ways and Means bill after the other plan fails, allowing the tax revision process to continue in the Senate. The House is dominated by Democrats, and the GOP alternative is expected to be overwhelmed.

"We think the Ways and Means bill can be passed," a White House official said.

The administration's private message is political: The defeat of the Ways and Means bill would be a victory for the Democrats and a black eye for the Republicans, who would stand accused of blocking their president's chief domestic initiative.

"The Democrats win either way; we win only if a bill emerges from the House," said a senior administration official.

Both bills would reduce personal and corporate tax rates while eliminating or curtailing many deductions and credits. The Republican plan has a top individual tax rate of 37 percent, while the Democratic bill would cut the top rate to 38 percent from its current 50 percent.

House Republicans spent much of yesterday trying to garner support for the alternative GOP package. In a party caucus, they presented figures calculated by the accounting firm of Ernst & Whinney showing that the level of itemized deductions allowed for families in the Ways and Means bill would be less generous than those permitted by the Republican measure.

The total tax cut for individuals in the Ways and Means package, however, is larger, at 9 percent, than the 7.4 percent cut proposed in the GOP plan.

Republican leaders looking for support for their plan faced considerable disunity, however. A letter to GOP members from four Republican legislators, including conservatives Vin Weber (Minn.) and Newt Gingrich (Ga.), said the GOP package was "only marginally different from the Ways and Means bill" and called for the defeat of both measures.

Lott said some Republicans probably will vote against both bills, and other GOP members said they disagreed with the notion that the Ways and Means legislation should be approved just to keep the process of tax revision moving.

"There is a great deal of cynicism in the minds of many Republicans as to whether the Senate can fix up the bill and make it better," said Rep. Bill Archer (R-Tex.).