The conservative southern Democrats whose votes were crucial to President Reagan in passage of his budget last year are so far keeping hands off the new budget he has embraced.

Leaders of the Conservative Democratic Forum--the so-called Boll Weevils in the House--yesterday said they see a lot of problems with the budget resolution that emerged Thursday from the Senate Budget Committee, with Reagan's approval.

They called it a step in the right direction, but made it clear that they will work on an alternative that may differ substantially from the latest Republican version.

Last year the conservative Democratic bloc in the House leaped aboard Reagan's bandwagon, breaking with its party and providing key votes in the Republican president's big first-year victories on spending and tax issues.

This year those Democrats intend to work, at least for the time being, with other House Democratic leaders and are trying to put together a version broadly acceptable in the House.

"It's safe to say, that package will have to be reworked on the House side," said Rep. Charles W. Stenholm (D-Tex.), a leader of the forum, referring to the plan first developed by Sen. Pete V. Domenici (R-N.M.) and subsequently embraced by Reagan.

Stenholm praised Domenici for breaking a deadlock, but said the new plan is "hazy and it has a lot of unanswered questions."

He also said the plan developed by Domenici "does not address the fairness question as well as it should have" because it does not offer enough protection for people of low incomes. "It almost accepted 100 percent of the first Reagan budget's cuts," Stenholm added.

On the other hand, Stenholm and his colleagues contend the new plan also does not reduce future budget deficits sufficiently, even though it envisions lowering the next three years' deficits by $416 billion from the levels estimated otherwise.

Rep. Buddy Roemer (D-La.) said he regards the $106 billion deficit projected for fiscal year 1983 in the Domenici plan as too high. "That's too high, but the trend is healthy," he said yesterday. "I'd prefer one about $95 billion."

The Boll Weevils have agreed among themselves on a budget proposal and have submitted it to Rep. James R. Jones (D-Okla.), chairman of the House Budget Committee. Stenholm and Roemer made it clear yesterday they intend to work initially through that committee and with other House factions to come up with a House budget a majority can accept.

The conservative Democratic group is in a strategic position this year insofar as the administration is concerned. A substantial number of moderate and liberal House Republicans will not support the president's present plan because of its freezing of major social programs, such as education, and the still large increases in defense spending.

With the House leadership strongly opposing the president, the administration would have to attract a large number of southern Democrats to prevail.

The Boll Weevils refuse to say at this point precisely what changes they would make. Stenholm indicated he would hold down spending by trimming back on the automatic cost of living features in some programs, including Social Security.

His objective, he said, is to produce a Social Security plan that will aid the elderly poor without giving money to older persons who are well off.

It is not clear how the southeners expect to raise additional revenues to meet their requirement of a lower deficit. Other Democrats in the House have insisted on repealing the third year of the tax cuts approved last year.

Stenholm said his group's plan so far assumes going ahead with the third-year tax cut. "But that is not set in concrete," he added.