Despite President Reagan's brave talk about "taking names" of those who voted against his budget-balancing amendment in the House and of mounting a campaign offensive against Democrats on economic issues, political reports reaching the White House portend a Republican disaster in the congressional elections only a month away.

"The people talking about us losing only four or five seats, the people saying we'll lose only 10 or 15 -- they just don't know what is going on out there," a high-ranking White House official acknowledged last week. While GOP officials are talking optimistically for fund-raising purposes, this official said, the unemployment issue is undercutting Republican congressional candidates.

This new White House assessment, contradicting earlier rose-colored analyses, comes from field reports and White House polls. It has filtered up to the president and is believed to be the reason he tried to lower GOP expectations for the mid-term elections at his news conference last week.

Many Democratic candidates still avoid knocking Reagan directly, preferring to run against Reaganomics rather than a president more popular than his policies. But there is no evidence that Reagan's popularity has done much to prevent the phenomenon known to pollsters as the "return of the native," which means that normally Democratic blue-collar voters who supported Reagan in 1980 are returning to their traditional partisan allegiance.

The president is concerned enough about what is happening that he has postponed this week's western trip for a day so he can speak Wednesday to GOP candidates trooping here. But it is likely to take much more than a presidential pep talk to prevent a Democratic congressional landslide in November.

The revised Reagan schedule this week calls for a speech in Reno, Nev., Thursday, seeing the Joffrey Ballet in Los Angeles that night and meeting with Mexican president-elect Miguel de la Madrid in San Diego on Friday after a wreath-laying ceremony in Tijuana the same day. Reagan is to spend the weekend at his ranch in the Santa Ynez mountains and address a fund-raiser in Dallas next Monday for Republican Senate candidate James Collins.

Don't look for any close encounters with the fourth estate at any of these campaign appearances. Learning their lessons from the problems Reagan created for himself with off-the-cuff remarks in the 1980 campaign, the president's advisers are keeping him away from the press in an effort to restrain him from giving stray answers to pointed questions. When the president went to the Capitol for the balanced-budget amendment rally last week, the press pool accompanying him was deliberately kept half a block away.

The president has asked for accelerated planning by the National Security Council and the State Department on developing what he calls "concrete steps" for withdrawal of both Israeli and Syrian forces from Lebanon. An administration official said over the weekend that Reagan feels that momentum exists for withdrawal but that a timetable is lacking.

"When am I going to start seeing actual planned steps in the phasing of withdrawal?" Reagan was quoted as saying. U.S. officials are to meet this week with Syrian and Israeli envoys to press the point.

Although no one has told her formally, word in the White House is that longtime Reagan loyalist Helene von Damm will be the next U.S. ambassador to her native Austria. Von Damm, the White House personnel director, goes back with Reagan to his California days when she worked first for William P. Clark when he was Reagan's executive secretary and then as personal secretary for Gov. Reagan. Von Damm, whose 81-year-old mother lives in Austria, is fluent in German.

Von Damm has been quietly interviewing women business executives to build a backlog of names for prospective administration vacancies. "When a vacancy occurs, the white male network instantly produces half a dozen candidates," she said. "We have to recruit women and minorities."

A glowing tribute filmed by Reagan for retiring Rep. John J. Rhodes (R-Ariz.) included choice remarks never seen by the black-tie audience at the farewell dinner for the former minority leader Sept. 21. When the film was being made, White House cameramen ignored the "cut" signal and caught the president leaning forward into the camera after the tribute and ad-libbing, with mock anger: "Now I want to know why you voted to override my veto."

Told about the comment, Rhodes said it showed that Reagan has a sense of humor and actually keeps track of those who vote against him on key issues, in this case the House override of the president's veto of the supplemental appropriations bill.