House Democratic leaders yesterday gave qualified approval to President Reagan's $4.3 billion proposal for jobs and recession relief, but indicated they may seek more money now and definitely will push for a more ambitious recovery program later this year.

"This is not the best bill we Democrats could write, but it may be the best bill we can enact into law" immediately, said House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) as he pledged to put the legislation on a fast track for congressional passage within a couple of weeks, starting with mark-up of legislation next week by the House Appropriations Committee.

Even with Democratic "modifications," the bill will "be in the ballpark of what the president will sign . . . he'd have a hard time vetoing it," said O'Neill.

After meeting with the House Democratic Steering and Policy Committee on the jobs offer that Reagan made last week, O'Neill said the leaders "agreed that this proposal represents phase one in meeting our country's economic emergency."

But he added that the Democrats "will be looking to add in the vicinity of $1 billion or more" to the administration's proposal, including funds for summer youth jobs, low-income energy assistance and health care for women and infants.

And O'Neill and other Democrats emphasized repeatedly that the proposal will be considered only as an "emergency" first step, to be followed shortly by more comprehensive job-creating legislation which they have not yet spelled out.

"It's not a jobs bill . . . it's an emergency bill; it's acceptable only on that basis," said Rep. Augustus F. Hawkins (D-Calif.), a leading champion of bigger jobs legislation.

After the White House reacted with annoyance to O'Neill's public discussion of the proposal and his suggestion of a $1 billion add-on, Rep. Thomas S. Foley (D-Wash.), who is spearheading the jobs effort, cautioned reporters against overemphasizing points of disagreement between the administration and House Democrats, including the extra $1 billion. Democrats "want agreement, not confrontation," he said.

But Foley also sought to put down Reagan's claim that the $4.3 billion offer amounts to just a speed-up of old commitments that will add little, if anything, to cumulative budget totals. "It's almost all new money as far as we're concerned," said Foley, adding: "We are not discounting this against future years."

As summarized by the Democrats, Reagan's offer bears a strong resemblance to the slightly larger jobs package that the House approved in the lame-duck session late last year and then shelved in conference under threat of a veto from Reagan, who castigated what he called "make-work" jobs in the bill.

For jobs, it includes $2 billion in additional funding for mass transit, highways, soil conservation and flood control construction projects; $1.2 billion in accelerated spending for community development and urban development grants to local governments for maintenance and construction projects; $765 million for repair of federal buildings, military housing, prisons and related facilities, and $50 million for operation of day-care centers.

For humanitarian aid, it includes $250 million for food and shelter, including funds for distribution of commodities.

The House Democrats' jobs bill totaled $5.4 billion, which is roughly what the bill would add up to with a $1 billion add-on.

In all, the package would cost $7.6 billion, including nearly $3 billion to fund extended unemployment benefits through Dec. 31 and $276 million for related employment services.

O'Neill and Foley were not shy in pointing out that Reagan, in making his offer, has moved considerably toward the Democrats' position that the government should take a more active role in creating jobs, in light of continuing double-digit unemployment, now 10.4 percent.

"In the past, the president has thought that a compromise meant that he received 80 percent of what he wanted," said O'Neill. "In this case, the people who want to see jobs and emergency [relief] received the better deal."

Senate Democrats, who also met with O'Neill on the plan, said much the same thing, while still objecting that the proposal was too small and insufficiently targeted at the long-term unemployed and at areas of highest unemployment. "At least it's something . . . it opens the subject for negotiations," said Sen. Carl Levin (D-Mich.), who is leading the Senate Democrats' jobs-planning effort.

Levin said there was also discussion of another $1 billion add-on for jobs spending targeted to reflect the most serious needs, although others said that targeting of money already in the package was probably more likely if any such modifications are going to be made.

Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), who along with other Senate Republicans got the jobs talks started with the White House, said he was "delighted" with the progress so far. "I applaud the speaker," he said.

At the White House, deputy press secretary Larry Speakes indicated that the administration was miffed at all the chatter on Capitol Hill about the offer, saying, "It was our understanding that the [Democratic] leadership would respond privately and directly to us . . . . We, for our part, intend to keep the discussions private so long as they hold the promise of being fruitful."

Meanwhile, a House Agriculture subcommittee yesterday began hearings on an emergency farm credit bill designed to help farmers cope with what the chief sponsor, Rep. Ed Jones (D-Tenn.), called "the worst agricultural crisis in the last half century."

The bill would provide additional operating-loan money for the Farmers Home Administration and allow farmer-borrowers deferrals on loan repayments if they can meet certain conditions. Jones and Rep. E. Thomas Coleman (R-Mo.), the chief co-sponsor, indicated they plan to move the bill quickly to the full committee, where easy approval is expected.