This is nail-biting time on Capitol Hill for the 21,000 Senate and House employes who are waiting to see what kind of a pay raise--if any--their bosses will give them this year.

Pay raises for most of the government's million-plus nonsupervisory white-collar workers are automatic. They get a 4 percent raise this month unless they make $57,500 or more, or are under the merit pay system used to "reward" managers and supervisors.

But there is no automatic pay raise on Capitol Hill. Members can give employes the full raise or more, half a loaf, or nothing--so long as they stay within their office budget.

Payroll changes for the 13,000 House of Representatives employes are supposed to go into the payroll office Friday. Workers who are too timid to ask their bosses about the raise will have to wait until the 29th when they examine their monthly checks to see what surprises they hold.

Most of the Senate's 8,000 workers get paid twice a month--on the 5th and the 20th. Like the House side, senators and committee chairman have complete discretion to grant, or withhold the pay raise. Their word is law.

Congressional staffers say that most members use their discretionary authority, which accounts for the fact that pay scales for the same jobs vary widely on Capitol Hill. It is the rule, they say, not the exception for members to give some employes bigger raises than others.

Asked if there are some members who are known as tightwads, a veteran House staffer said. "Absolutely, yes!" Asked if he would care to name any of them he said: "Absolutely, no!" How about off the record, for deep background? "Have a nice day," he said.

Federal/Military Pay Raise: A number of federal and military outposts still have not received official notification that the 4 percent pay raise is in effect. It is. President Reagan signed the executive order (No. 12387) on Oct. 8.