The Republican platform committee last night approved a 1980 platform that proposes huge immediate increases in defense spending, total decontrol of all energy prices and a three-year program of tax reductions for all Americans.

The platform holds firmly to a conservative line on big issues and small, from recommending an elaborate variety of new weapons programs to favoring use of the death penalty, and repeal of the 55 mph speed limit.

The platform was tailored to suit Ronald Reagan, the man Republicans will nominate as their 1980 candidate here next Wednesday night.

But the document may also please President Carter and his partisans, because it advertises Reagan's close identification with right-wing positions on most of the controversial issues of the day. Carter clearly hopes to depict Reagan as an extremist in the fall campaign.

Delegates on the platform committee repeatedly rejected proposal to water down or restrain their most conservative instincts for the sake of appealing to more voters in November. Today, for example, they voted to pledge a Republican president to nominate to the Supreme Court only people who "respect traditional family values and the sanctity of innocent human life," meaning only people who oppose abortion.

A lone delegate from Hawaii, John Leopold, said this plank represented a submission to "single-issue politics that would only alienate many Americans. The plank was then adopted by an overwhelming voice vote.

Wednesday the platform committee approved planks recommending a constitutional amendment to ban all abortions and retreating from support of the Equal Rights Amendment.

The defense plank in the new platform, drawn up after close consultations with Reagan campaign aides, is the most detailed statement yet of the kind of expanded defense program the Republicans will recommend during the fall campaign.

Though its drafters studiously avoided putting any price tag on their plans, they would, if implemented, cost a minimum of $15 billion more in the first year's Pentagon budget, and probably more like $25 billion to $40 billion.

The defense plank calls for accelerated development of all the United States' new missile systems, construction of a new intercontinental bomber, deployment of a new air defense system, construction of large numbers of new planes and warships, a big investment in the reserves and many other new initiatives.

This long list raises the prospect of political controversy, particularly when it is given a cost estimate. Despite the emergence of a new congressional consensus for more defense spending in recent weeks, the idea of besting President Carter's own proposals for new spending by an immediate $15 billion to $50 billion is bound to be hotly debated.

Richard V. Allen, Reagan's chief foreign policy aide, said in an interview here today that "it's wildly early" to propose a dollar figure for the defense programs Reagan would initiate if elected. "I've asked our defense advisers to go back to square one" to produce a precise range of dollar estimates for possible defense initiatives, he said.

Allen noted that an important plank in the platform calls for spending substantially more on the volunteer Army in hopes of making it work better, and that this alone could eat up as much as $6 billion a year.

Rep. Jack Kemp (R-N.Y.), who was chairman of the committee that drafted the defense plank, said he thought it might cost an immediate $15 billion in next year's budget, if Reagan is elected. He said he thought higher estimates were unrealistic.

But a group of congressional staffers who have proposed military spending increases similar to those in the new Republican platform have estimated their first-year cost at nearly $40 billion.

On tax policy, the GOP platform echoes promises that Reagan has been making since the primaries began. The platform promises "across-the-board reductions in personal income tax rates, phased in over three years, which will reduce tax rates from the range of 14 to 70 percent to a range from 10 to 50 percent."

On energy, an issue that independent candidate John B. Anderson hopes to make a centerpiece of his presidential campaign, and which President Carter is already trying to exploit, the Republicans today approved an optimistic plank promising the country that energy shortages can be made to disappear.

Adopting a thoroughly free-market approach, the Republicans endorsed the desirability of immediate removal of all price controls on oil and gas, thus forcing conservation through substantially higher prices while simultaneously providing inducements for the production of energy from new sources that the Republican platform says are potentially available.

For good measure, the delegates today adopted an amendment offered from the floor that would have the effect of ending the federally enforced 55 mph speed limit by allowing the states to set their own limits at whatever level they would like.

Rep. Bud Shuster (R-Pa.) rose to oppose this idea "reluctantly," explaining that he had learned on the House Transportation Committee that the lower speed limit saved millions of gallons of gasoline and, more important, thousands of lives because of reduced traffic accidents.

Sen. Malcolm Wallop (R-Wyo.) made a similar point, arguing that the country needed national policies that had the effect of reducing oil consumption.

But Rep. Dave Stockman (R-Mich.), a staunch free-market advocate who was a principal author of the energy plank, disagreed. The speed limit amounted to an artificial constraint on the consumption of oil, he argued, and was typical of Democratic attempts to solve the energy problem by ordering people to cut back. With Stockman's help, the proposed plank was easily adopted by the full committee.

The GOP energy plank includes strong support for increased use of nuclear power."The Three Mile Island accident suggests the need for certain reforms," the plank says, "but illustrates that even under improper operation, nuclear plants do not endanger public health or safety."

The GOP platform includes numerous references to the need to reduce government spending, cut back on government regulations and return more power to states and localities. It specifically endorses an increase in "block grants" of federal funds to local governments, which can be used for whatever purpose they choose, in place of categorical grants, which can be spent only on specific programs.

The plank on welfare specifically recommends the block grant approach, while opposing any federal assumption of the states' welfare responsibilities. The object of welfare policy should be to "help return control of welfare program to the states," the plank says, a position in complete accord with Reagan's campaign rhetoric.

The platform contains no list of government programs to be cut back or eliminated, however. It recommends that a high-level commission of distinguished citizens evaluate the entire executive branch and propose cutbacks. In one area that is specifically considered in the platform, federal aid to veterans, the Republicans endorse an expensive increase in benefits.

The generally conservative delegates here seemed much more interested in social issues like abortion and the ERA than in the traditional "big government" concerns of earlier generations of Republican conservatives. One indication was the nearly unanimous support given today to a plank on environmental protection that was offered from the floor by Jan. A. K. Evans of the District of Columbia.

This plank explicitly endorsed a governmental role to preserve the environment, while also noting many alleged excesses in governmental enforcement policies. Stephen Danzansky, another D.C. delegate, acknowledged after it was approved that Evans had apparently slipped one past the conservative gathering.

Danzansky was one of several moderate delegates who expressed emotions ranging from eyebrow-raised bafflement to exasperation at the firm control the conservatives repeatedly demonstrated in the platform committee.

Their influence reappeared on all sorts of issues.For example, a plank on crime says Republicans will seek legislation to prevent government-financed lawyers employed by the neighborhood legal services program from defending poor people who are "repeat offenders" or accused of "pushing or smuggling" drugs.

On foreign policy, the platform reflects all of Reagan's traditional views.

It clarifies his position on the question of Taiwan, recommending continued cooperation with the Peoples Republic of China and avoiding any call to reestablish full relations with Taiwan.

The platform calls for a much tougher policy toward the Soviet Union, and specifically rejects as unacceptable the Strategic Arms Limitation Treaty (SALT II). It calls for a much stronger U.S. intelligence establishment, and suggests changes in the Freedom of Information Act "to reduce costly and capricious requests to the intelligence agenices" for information.

On the Middle East, the platform declares that Israel's security "is a moral imperative and serves the strategic interest of the United States." In a platform that is filled with seathing criticisms of President Carter, this plank says simply what "a Republican administration will encourage the peace progress between Egypt and Israel and will seek to broaden it."