House Republicans, trying to position themselves as the party of "new ideas," yesterday released a 252-item wish list for the new Congress that endorsed tax simplification, a freeze on U.S. contributions to the United Nations and a minimum length for the school day.

They called for a constitutional amendment requiring a balanced budget, but ruled out two of the most commonly suggested methods of achieving it -- tax increases and defense cuts.

They held out for tax simplification. But if that fails, the document proposes a variety of new tax credits that would cost the government money. These include breaks for day care, home care for the elderly, and training and hiring of "displaced homemakers."

The Republicans conceded yesterday that many of the proposals, including dozens pushed unsuccessfully by President Reagan in his last four budgets, were likely to go nowhere in the House, where Democrats outnumber Republicans 252 to 182, with an Indiana seat still vacant.

But the package will show that "the Republicans are interested in laying claim to new ideas," said Rep. Jerry Lewis (R-Calif.), chairman of the House Republican Research Committee, which drafted the package.

In a toughly partisan introduction, the Republicans charged that the "new ideas" coming from younger members of the Democratic Party are simply "antiques touched up with varnish and gilt."

The document, titled "Ideas for Tomorrow; Choices for Today," was begun before last November's elections when it appeared that the Republicans might win enough seats to take de facto control of the House.

More moderate than the platform adopted by the Republican Party at its presidential convention last August, the document sidesteps the subjects of abortion and school prayer. At the same time, it refers to America as a "rainbow coalition" -- the rallying cry used by Jesse L. Jackson throughout his presidential campaign.

Lewis said yesterday that some of the more controversial social agenda items mentioned in the platform were not included in the "Ideas" package because "I didn't want some people's choice of sensational headlines on these controversial issues to weigh down the effort to highlight these new ideas."

"This is a legislative document, not a political, ideological document" for the party faithful, said one high-ranking House Republican. "You don't implement platforms. Platforms are put in windows for people to see as they walk by."

The "Ideas" package does not deal with the rising costs of entitlement programs, including Social Security. Lewis said the Republicans expected to put out a separate document on that subject.

Minority Leader Robert H. Michel (R-Ill.) and others yesterday said House Republicans were unlikely to agree to a freeze this year on Social Security cost-of-living adjustments (COLA). Senate Republicans are considering such a freeze as part of a deficit-reduction package. Reagan, who campaigned for reelection on the promise that he would not cut Social Security, said last week that he would consider the COLA freeze if it were supported by a strong bipartisan coalition in Congress.

The document proposes:

* A modified flat tax proposal, along the lines proposed by Rep. Jack Kemp (R-N.Y.) and Sen. Robert W. Kasten (R-Wis.) or the Treasury Department, that would eliminate most tax deductions but dramatically lower and simplify rates.

* Substantial spending reductions, possibly along the lines President Reagan is expected to propose in his fiscal 1986 budget.

* A "pay-as-you-go" system that would require that a new program have a source of funding, such as user fees, or be financed by cuts in an existing program. Republicans rejected this approach last year when it was incorporated into a Democratic budget resolution.

* Presidential line-item veto power over appropriations bills. In addition to a constitutional amendment granting this and requiring a balanced budget, the Republicans proposed a constitutional amendment requiring a two-thirds vote of Congress to pass all appropriations and budget measures. The Republican proposal also recommended restoring limited presidential impoundment authority.

* Enactment of a subminimum wage for young people.

* Adoption of the Reagan administration's enterprise zone legislation, which would provide breaks to businesses that locate in depressed areas.

Changes in welfare requiring under-age unmarried mothers to live with parents or legal guardians to receive welfare. The Republicans also want to require states to adopt workfare programs in which able-bodied welfare recipients must perform community work.

* Enactment of legislation to control illegal immigration.

In a civil rights section of the document, the Republicans recommended fines and prison sentences for those convicted of destroying or stealing religious property.

The "Ideas" package also proposed:

* Legislation to make it easier to use evidence obtained in illegal searches.

* The death penalty for murders committed by federal prisoners serving life sentences; mandatory life sentences for those found guilty of kidnaping children; the death penalty for cases where a kidnaped child died as a result of the crime.

* A mandatory minimum length of the school year, as well as the school day, as a condition for federal aid. The aid would also be contingent on a system for student promotion based on achievement and attendance, and a merit pay system for teachers.

Other education proposals included allowing families to set up a tax-deferred savings accounts for post-secondary educational expenses of children and tuition tax credits for families who send their children to private schools.

On defense, the package proposed funding for development of the Stealth bomber, continued deployment of the MX nuclear missile, upgrading of Minuteman missiles, research and development of the Midgetman missile and acquisition of 99 B1 bombers by fiscal year 1988.

In addition, the House GOP proposed lifting the ban adopted by Congress last year limiting to three the number of tests that can be conducted with antisatellite space weapons.

In foreign relations, the Republican package backed continued funding for the rebels fighting the leftist government of Nicaragua and economic and military aid to El Salvador, Honduras, Guatemala, Costa Rica and other "friendly South American nations.