President Reagan last night proposed a three-year standby tax increase beginning in fiscal 1986 if the federal budget deficit does not come down to acceptable levels. The increase would be a 1 percent surcharge on individual and corporate taxable income and a $5-per-barrel excise tax on oil, which could raise gasoline prices an estimated 12 cents a gallon.

In other deficit-reducing steps, the president proposed for the next year:

* A 12-month freeze of federal civilian and military pay and of federal retirement benefits; this would mean no federal pay raise this coming October.

* A six-month delay in cost-of-living adjustments in all federal programs tied to inflation, including Social Security, federal aid to the aged, blind and disabled, and veterans' benefits.

* Freezes and cuts in other domestic spending programs, including "reforms" in civil sevice retirement, so that as a whole they would decline after allowing for inflation. Defense spending, however, would continue to rise.

Even with all these efforts to close future budget gaps, administration officials said the budget Reagan sends to Congress next week will project a deficit of $189 billion for fiscal 1984, which starts next Oct. 1, declining to $117 billion by fiscal 1988. This year's likely deficit will exceed $200 billion, they said.

Reagan also proposed:

* New tax-free Education Saving Accounts in which parents could set funds for their children's college education. Details of how this might work were not provided last night.

* Through block grants to the states, a new program designed to increase the number of teachers proficient in science and mathematics instruction at the high school level.

* A new employment bill that would include the extension for six months of supplemental unemployment benefits for those who have exhausted their regular and extended insurance coverage.

* A "broadened" international trade strategy designed to move more U.S. goods into foreign markets.

The president also proposed, as expected, initiatives to hold down health care costs by limiting future Medicare payments to hospitals while requiring patients to pick up a large share of the Medicare load.

But, at the same time, he recommended catastrophic insurance coverage for Medicare recipients so the government would pay full costs above certain fixed amounts each year.

He also included proposals to step up the government's fight against organized crime and drug trafficking, and remedy inequities based on sex in employer pension systems, among others.

He called generally for "ways to simplify the tax code" but proposed no specifics.

Reagan also appealed to Congress for a host of initiatives that failed in his first two years in office, including tuition tax credits, enterprise zones, a crime bill and a constitutional amendment to allow voluntary prayer in public schools.

But absent from this year's list was the constitutional amendment to balance the federal budget that Congress rejected last year.

Administration officials said last night that the president will send to Congress next week a fiscal 1984 plan in which spending authority grows only 5 percent next year--which would mean no growth overall after estimated inflation.

This was portrayed as a "freeze" by these officials but they acknowledged that the spending plan actually will allow defense budget authority to rise 14 percent before inflation and everything else to grow only 2 percent. After inflation, expected to be about 5 percent, that translates into an overall 3 percent cut for domestic spending and a 9 percent increase for military spending authority.

The defense increase would occur despite the $11.3 billion reduction agreed to earlier this month by the president in originally projected 1984 spending authority.

The administration officials said Reagan would not seek legislation to put the standby tax increase on the books immediately.

Rather, they said this would depend on whether the fiscal 1986 deficit as projected by the administration on July 1, 1985, seems likely to be more than 2.5 percent of the gross national product. This means that, to avoid the tax increases, the deficit then would have to be projected at less than about $120 billion. That is thought highly unlikely; the standby taxes were conceived in the first place as a device to let the president show deficits declining in later years to levels that would not shake the money markets.

The officials said the provisional tax increase would also be contingent on congressional approval of the administration's proposed budget cuts and freezes, although they stopped short of saying total cooperation from Capitol Hill would be necessary.

A third "trigger" for the taxes is a requirement that the economy be expanding on July 1, 1985, which is three months before fiscal 1986 begins.

As outlined last night, the tax increases would be limited to three years and to a maximum of 1 percent of GNP--or between $40 billion and $50 billion--each year.

Under the surcharge proposal, taxpayers would pay the same 1 percent of taxable income regardless of their income level.

Both this and the oil excise tax will be extremely controversial. The oil tax, in addition to its price effect, is likely to divide Congress along regional lines between producing and consuming states.

One proposal not included in Reagan's speech last night but still under consideration would establish a voucher system for using federal school aid. Officials said this may be proposed later.

The employment proposals Reagan outlined will be sent to Congress as new legislation that will include a sub-minimum wage, or "youth differential," for teen-agers during the summer months. The new package, in addition to the added jobless benefits, will also include tax credits for employers who hire the long-term jobless; allow states to use their unemployment benefits for job retraining and relocation, and additional money for the job training bill Reagan signed last summer.

The president also plans to seek again from Congress the regulatory reform bill that failed to make it through the last session, and officials said the administration "will explore" the adoption of a "mechanism" allowing Congress to review regulations "on a periodic basis."