WASHINGTON, March 14 - Senate Republicans on Tuesday narrowly defeated an effort to impose budget rules that would make it harder to increase spending or cut taxes, a move that critics said that showed Republicans were posturing in their calls for greater fiscal restraint.

In the first of several politically charged budget and spending issues confronting Congress this week, the Senate rejected on a 50-to-50 tie a proposal to restore what are known as "pay-go" rules, a requirement that tax cuts and some new spending be approved by 60 votes or offset by budget savings or revenue increases.

Democrats and a handful of Republican allies said that the added discipline was essential to getting a handle on the mounting federal debt and that the rules had been instrumental in reducing red ink before they were allowed to lapse in 2002.

"For those who say they are fiscally responsible, here is your chance," said Senator Kent Conrad of North Dakota, senior Democrat on the Budget Committee. "You are going to be able to prove with one vote whether you are serious about doing something about these runaway debts and runaway deficits or whether it is all talk."