Senate Democrats yesterday stalled a farm spending bill by tacking on their so-called patients' bill of rights, vowing to attach it to every possible piece of legislation until they are promised a vote on their proposed HMO reforms.

Majority Leader Trent Lott (R-Miss.) had to temporarily withdraw the $60.7 billion appropriations bill for the Agriculture Department shortly after Sen. Byron L. Dorgan (D-N.D.) offered the bill on health maintenance organizations as an amendment. Lott warned that the Democrats' action would hurt farmers, but Democrats said they will keep holding up unrelated bills as long as GOP leaders stall their health plan.

At the same time, House Democrats led by Rep. Steny H. Hoyer (D-Md.) have threatened to load another spending bill with gun control provisions that failed last week unless congressional negotiators agree to include them as part of juvenile justice legislation.

The provisions, which include new rules for background checks at gun shows, a ban on the importation of large-capacity ammunition clips and a requirement that safety locks be sold with new guns, would be offered as amendments to the fiscal 2000 spending bill for the Treasury and general government agencies.

Fearing a reprise of last week's divisive gun debate, House Appropriations Committee leaders are likely to put off consideration of the Treasury bill until after the July 4 recess.

HMO reform and gun control are the latest in a series of controversies that have complicated the annual appropriations process and enhanced prospects for another legislative train wreck this fall. House conservative activists, led by Rep. Tom Coburn (R-Okla.), added weeks to the process by demanding and getting modest reductions in next year's agriculture and legislative branch spending, and conservatives are expected to demand even larger cuts in a transportation spending bill this week.

With the Republicans holding narrow six-vote majorities in both chambers, even a handful of members can exert enormous pressure on the leadership. Now the Democrats are getting into the act.

Polls suggest that a vast majority of Americans want stricter regulations on managed-care plans, and Democrats believe HMOs are a winning political issue for them.

"The time has come to debate these issues before the American people," said Sen. Edward M. Kennedy (D-Mass.). "The time has come for votes on these critical issues. The time has come for the Senate to fulfill its duty to protect American families."

Lott pledged to allow an open debate on HMO reforms sometime in the future and praised a less sweeping and less expensive Republican version of the patients' bill of rights. Three-fourths of all privately insured Americans are enrolled in managed-care plans, and the GOP is also eager to claim the mantle of HMO reform. But Lott was clearly irked by the Democrats' amendment and ordered the Senate clerk to stop reading it aloud.

"I find that our Democratic colleagues have put the Senate in an unfortunate position by offering this bill at this time," Lott said. "The pending bill is a very important agricultural appropriations bill. . . . For some reason, the Democrats have decided to ignore the needs of the American farmer and turn this into a health care reform bill."

Democrats also are hitting hard at the gun control issue in the wake of the Littleton, Colo., high school shootings. The House last week voted to reject the gun control package, but the Senate adopted gun control measures, including a tougher gun show provision, as part of its juvenile justice bill. Negotiators from the two chambers must work out a compromise.