Democrats blinked in the 100th Congress' first test of wills yesterday with President Reagan over arms control as House leaders abandoned efforts to use a long-delayed catchall spending bill as leverage to force the administration to resume compliance with the unratified SALT II treaty.

The retreat, prompted by veto threats and Senate Republican pressure tactics, came as Congress appeared torn over how to deal with the administration's Persian Gulf policies. It indicated that the president retains considerable clout on Capitol Hill despite the Iran-contra affair and other problems.

Asked whether the Democratic-controlled Congress was beginning to look like a "paper tiger" on such key national-security issues as arms control and the Persian Gulf, House Speaker Jim Wright (D-Tex.) responded, "That is a risk we take in our efforts to be really bipartisan."

The decision by Wright and other Democratic leaders to drop their insistence on immediate action on SALT II compliance broke an impasse over the omnibus spending bill, which was then approved by a House-Senate conference committee and put on track for final approval by Congress next week.

More than half the $9.4 billion bill is allocated to resumption of the farm-subsidy and crop-loan program that ran out of money nearly two months ago, with most of the rest earmarked for scores of other programs that would run out of funds before the fiscal year ends Sept. 30.

The supplemental bill also includes new initiatives ranging from $355 million to feed and shelter the homeless to $300 million for economic assistance to Central American democracies and $50 million for the Philippines.

Among other provisions were compromise restrictions on drug-testing for federal workers and procedural precautions to phase in employer sanctions under the new immigration law. A dispute over whether to halt further funds for construction of the U.S. Embassy in Moscow was left to be resolved by the two chambers when they taken final action on the bill.

Removal of all reference to arms control eliminated the administration's biggest objection, but there was still no definitive word from the White House late yesterday whether the president would sign the bill, which contains other features that the administration opposes.

In explaining House leaders' decision to drop the SALT II provision, Wright cited the "urgent need to provide funds for the Commodity Credit Corp. farm programs and for aid to the homeless." He also said the House had won assurances from Senate leaders, including Majority Leader Robert C. Byrd (D-W.Va.), that the Senate will vote on the treaty compliance issue this year.

"With that assurance and the support of Majority Leader Byrd, we feel certain that this vital issue will be fully and clearly addressed by the Congress this year," Wright said.

It is unclear when and how the Senate will vote on the issue, however. Senate Republicans have been holding up consideration of a defense-authorization bill for next year on a separate arms-control issue that would bar expanded testing of the administration's Strategic Defense Initiative (SDI). They have indicated they will stall on the SALT II issue as well. But arms-control provisions could also be attached to appropriations bills, including an omnibus "continuing resolution" that would have to be passed by Oct. 1 to keep the government from closing down.

Senate Republicans had been using a threat of similar obstruction tactics -- and the threat of a presidential veto -- to force House Democrats to drop their SALT II proposal, which was aimed at reversing the administration's 1986 decision to stop adhering to weapons limits in the decade-old agreement with the Soviet Union. If the spending bill included the SALT II provision, which would have required the administration to resume adherence to the weapons ceilings, GOP senators were prepared to object to a budget waiver for the bill.

A budget waiver requires 60 votes, and Democrats control the Senate by only 54 to 46. Republicans could also block the measure with a filibuster, which would also take 60 votes to break.

The House had also approved a ban on testing of all except the smallest nuclear weapons, but shelved the more-controversial testing ban proposal earlier in their negotiations with the Senate in hopes of concentrating on the SALT II provision.

The House has included SALT II, test ban and SDI restrictions in its version of the defense authorization bill for next year. But there is no guarantee of Senate action on the measure so long as Republicans can sustain a filibuster against it.

While relenting on the SALT II language in the spending bill, Wright sharply criticized the president for breaching the treaty's weapons limits, calling it a "quixotic, foolish gesture . . . to thumb his nose at the Soviet Union . . . and show machismo." Wright said he wanted to pursue a bipartisan approach on the issue but found "utterly no cooperation" from the administration.