Congressional approval of President Bush's new budget would allow the Internal Revenue Service to increase the number of tax returns it audits _ but not by much. IRS Commissioner Fred T. Goldberg Jr. told reporters the agency anticipates auditing 102 returns per 10,000 that will be filed in 1990 and 103 per 10,000 next year. That compares with an all-time low of 97 per 10,000 returns for the 1989 tax year. ``The fact remains that there has been a continuing decline in audit coverage for a number of years, but now we are seeing a reversal of the trend,'' Goldberg said after Bush's proposed budget for the 1991 fiscal year was made public Monday. Although IRS officials agree that more returns should be audited, they point to concerted efforts over the past few years to target larger returns, those involving tax shelters and others likely to yield more revenue. Even so, Goldberg said, the audit statistics do not tell the whole story. He noted, for example, about 40 million couples and individuals file returns that are based almost entirely on income from wages, interest and dividends. IRS computers now automatically check those returns against backup documents filed by employers, banks and brokers to ensure that all income is reported. While those computer matches are not audits, Goldberg said, they are thorough enough to make it difficult for taxpayers to under-report such income. The agency's proposed budget for 1991 is $6.14 billion, up 11.6 percent from this year's $5.5 billion. A big part of that increase represents another installment on the agency's plan to replace an outmoded computer system. Goldberg said the new system will cost up to $6 billion over the next decade. One aim of the new system is to allow taxpayers to get answers to questions about their tax accounts as easily as they get information about a bill from a credit card company. The Bush administration estimates the IRS will collect an additional $3 billion next year because of management initiatives and the increase in the agency's own spending. Goldberg said the IRS will spend an additional $56 million and assign about 1,000 new staff members to reducing accounts receivable from a record level of nearly $60 billion. Those are taxes that have been assessed but not paid. The agency expects to spend $330 million in the new year for taxpayer service, which includes answering telephoned tax questions. That figure is up from $317 million this year, principally because last year IRS employees gave the wrong answer to one of every three telephoned questions.