Sen. Lowell P. Weicker Jr. (R-Conn.), chairman of the Senate Small Business Committee, told Senate Republican leaders Friday that he thinks he has the votes to save the Small Business Administration, according to sources.

Under Weicker's proposal, most of the agency's direct business loans would be eliminated, but those for minorities, Vietnam-era veterans and the handicapped would be retained. Loan guarantees would be retained, but all nonphysical disaster loans would be eliminated, as well as loans to farmers hurt by natural disasters. The agency's field structure and management assistance programs also would be retained.

Reliable sources said that Weicker told Senate Majority Leader Robert J. Dole (R-Kan.) and Senate Budget Committee Chairman Pete V. Domenici (R-N.M.) that he had a bipartisan coalition of 47 senators lined up and that he probably could win a floor vote.

The Reagan administration has called for abolishing the agency, eliminating about half its functions and shifting the rest to other agencies.

Meanwhile, in the House, Rep. David Dreier (R-Calif.) continues to lead the Republican effort to shut down the SBA.

"Most businesses would rather see a $5.3 billion reduction in the federal deficit rather than the continuation of any program that the SBA offers," Dreier said. "What sense does it make to give Miami loans to offset the tourist dollars lost from accepting Cuban immigrants? What sense is there to giving ski lodges loans because there was a light snowfall? That's the kind of thing the SBA does best."

On the other side of the issue is Rep. Parren J. Mitchell (D-Md.), chairman of the House Small Business Committee. Early last week, Mitchell said he agreed that some direct lending and all nonphysical disaster loans could be eliminated, but that assistance for minorities, veterans and the handicapped should be retained.

Dreier said, "I don't believe we can continue to provide loans to veterans and the handicapped. Those funds are going to be available through other, private-sector programs." Dreier said that if they were not, the Health and Human Services Department should help the handicapped and the Veterans' Administration should aid veterans.

Last week, SBA Administrator James C. Sanders still was trying to sound like a member of the Reagan team, although aides said he had been working with interest groups and some members of Congress to save more of the SBA than the White House wants.

Sanders said, "I still believe that there are better money savers in the federal budget. I am still hoping that they the White House and Congress will devote more attention to those programs than to us."

PIKing YOUR FIGHTS . . . In April 1984, Congress said that any farmer who had been adversely affected by the Agriculture Department's payment-in-kind program should be eligible for disaster assistance from the SBA.

But when the SBA published its rules last year, eligibility was limited to those counties that had at least 25 affected agribusinesses. Farmers and members of Congress howled, and the SBA changed the rule. Now, the SBA wants to include only those counties where at least 20 percent of the farm acreage was adversely affected by PIK.

Still more howls.

On Capitol Hill, a bipartisan group, led by Nebraska members, is trying to overturn the new rules, saying they still don't comply with the intent of Congress.

Bernard Kulik, SBA's disaster assistance chief, said, "We have to have some rules and guidelines because there's only $100 million in funding this year in the pot." Sanders said that some on the Hill "would turn this into a new entitlement program. Some people want a sky's-the-limit type subsidy."