The House Budget Committee gave party-line approval yesterday to an old-fashioned Democratic budget for the next fiscal year that would defy President Reagan by raising taxes and social welfare spending while clamping down on the Pentagon.

With a highly unusual display of almost lock-step discipline, the panel's Democratic majority amiably but resolutely rolled over protesting Republicans and their claims that the $864 billion budget for fiscal 1984 amounts to a policy of "tax and tax and spend, spend, spend."

After two years of bobbing and weaving in the face of Reagan's tax and spending priorities, the Democrats came up with a budget, endorsed by Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass), that clearly restates old Democratic principles that had almost gone into hibernation.

But doubts were expressed by Democrats and Republicans alike about its future as it works its way through Congress, beginning next week on the House floor.

"Fellas, it ain't gonna wash," said Rep. Bill Frenzel (R-Minn.) of the Ways and Means Committee, which has already balked at raising taxes as much as the Budget Committee is proposing.

As outlined by the Democrats, the budget would provide:

* A 4 percent pay raise for military and civilian employes of the federal government, instead of the year-long salary freeze recommended by Reagan, along with a six-month instead of 12-month delay in cost-of-living increases in government retirees' pensions.

* Tax increases of $30 billion next year, enough to accommodate repeal of the 10 percent income tax cut scheduled for July 1, along with repeal of provisions that would index income tax rates to account for inflation after next year.

* A 4 percent increase in defense spending after accounting for inflation, instead of the 10 percent increase Reagan wants.

* A budget deficit of $174 billion, compared with Reagan's projected deficit of $189 billion, although Republicans complained that the practical effect would probably be higher deficits than those anticipated by the president, especially in light of dim prospects for a tax increase as large as the committee wants.

* A warning shot across the bow of the Federal Reserve in the form of an assertion that monetary policy must conform to growth and other economic assumptions in the budget, and a proposed new requirement that the Fed explain any discrepancies in an official report to Congress.

* Restoration of money for many of the social welfare programs that were cut by Congress at Reagan's behest in 1981 and 1982, along with a batch of new programs aimed at helping victims of the recession and providing for long-term employment growth.

Among these initiatives were up to $17 billion for job-creating efforts, money to help homeowners and farmers protect themselves against mortgage foreclosures, aid to protect the unemployed from losing their job-related health benefits and a new national industrial development bank for loan guarantees to industries in critical areas.

In addition, the budget proposes substantial restoration of money for programs ranging from child nutrition to services for the elderly, with especially large increases in education, health and employment services and programs for the poor.

Virtually ignored were Reagan's latest proposals for domestic spending cutbacks.

In many cases, in addition to spending increases for fiscal 1984, the committee proposed even larger increases in long-term budget authority, prompting Frenzel to complain: "What we're doing is putting a time bomb in the budget for future detonation."

In a preamble that read almost like a campaign manifesto, the Democratic majority on the committee accused the administration of having "rigidly adhered to a policy of helping the rich and penalizing the middle- and lower-income groups," and said:

"The critical problems of unemployment, business failures and inequitable treatments of the majority of our citizens demand a bold and imaginative Democratic plan to promote economic growth and fairness and equity."

As Republicans trotted out a series of amendments, especially on taxes, they were handily beaten back, nearly all on party-line votes of 20 to 11, also the vote by which the budget was adopted.

The closest vote, 10 to 8, came on a move to cut the size of the tax increase to $8 billion, which is what the Ways and Means panel has endorsed. Other moves, including one to wipe out the proposed $30 billion tax increase along with adjusting the budget to reflect legislation to repeal tax withholding on interest and dividends, were defeated 20 to 11.

Rep. Delbert L. Latta (R-Ohio) was even brushed aside when he objected to a committee vote on asking the Rules Committee to permit a Republican substitute on the House floor next week.

While Republicans were able to pick up enough conservative Democratic support to win budget victories for Reagan in the Democratic House during the last two years, Democratic gains in last November's elections make a duplication of that strategy exceedingly difficult this year, and the GOP has shown no enthusiasm for introducing a substitute.

"Our first job is to beat the Democratic budget," Latta said.

Republicans did not try to restore defense money that the Democrats proposed to cut, seeking instead to force them to explain where the cuts would be made. "It's a political decision, period," complained Rep. Tom Loeffler (R-Tex.).

In response, committee Chairman James R. Jones (D-Okla.) noted that the 4 percent increase was not out of line with a 5 to 6 percent increase under consideration by the Senate Budget Committee before it was reluctantly persuaded by Reagan to hold off action earlier this week.